Chandragupta Maurya
Origins:
He was son of King and Chief Queen of Moriya Nagar. Moriyas were descendant of Shakyas who tired of getting harassed by Viddhubha had come to a palace in Himalayas where the beauty of the place enchanted them and they established a beautiful city there.
When the King got killed by a rival feudal king, the Chief Queen who was pregnant along with her brothers came to Pushpapura (Patliputra). She delivered a son and to save him and hide his identity, she left him in a Cowpen where a bull named Chando protected him. The Gopa (Cow herder) and owner of the Cowpen found the baby boy and out of pity adopted the newborn baby. When he grew up a little, a hunter who was herder’s friend took him away to his house.
When he was grazing the cattle for the hunter, one day, Chanakya saw him playing Game of thrones with his friends and impressed by his leadership skills took him away promising a Kingdom.
Source- Mahavansh Tika
Another version is that when Chanakya was hiding from Nandas, he entered in a village of royal peacock tamers. The daughter of the chief of the tamers was pregnant and she developed a craving to drink the moon. If her craving wasn't satisfied, her body would abort the baby. Chanakya offered to help but demanded the baby in return. The family desperate to save the unborn child agreed to give up the baby. Chanakya arranged a method where the lady would drink the water which would have reflection of the moon. Her craving got satisfied and she delivered a healthy baby boy but chanakya didn't take the baby and left. The family named the baby Chandragupta.
Years later, he saw Chandragupta playing the Game of Thrones with his friends. Impressed by his leadership skills, he asked about his family. When his friends told him about his identity, Chanakya recognised he's the same boy he helped getting delivered from his mother's womb. He took the boy away promising him the Kingdom.
Source- Parishisth Parvan
Sandrocottus was from humble origins and he put prefects of Alexander to death and liberated Indians from servitude of the Greeks but ultimately brutally oppressed the people he helped getting liberated.
Source- Epitome of Justin
Sandrocottus was a stripling when he saw Alexander.
Source- Plutarch
Chanakya , his Guru , taught him for like Seven Years at Taxila and trained him to be a warrior and a King. One remarkable detail is that Chandragupta could hold his breath under water, so , he probably was given very intense military training.
Source- Mahavansh Tika and Parishisth Parvan
Chandragupta and Chanakya raised an army and attacked Patliputra but it brutally backfired. Their whole army got dismantled, many soldiers fled, many got captured and Chandragupta and Chanakya ran away. Soldiers of Nandas were after them. Chanakya saved Chandragupta’s life many times while running from Nanda army including one incidence where Chanakya disguised as an ascetic and he told Chandragupta to hide in the river. Chandragupta could hold his breath in water for a long time.
Chandragupta went inside the river and when soldier came he asked if he had seen a warrior and his mentor. Chanakya said he was hiding in the river and when soldier came forward, he was struck with a sword.
When chanakya asked, why did you hide under the water when I asked you to. Chandragupta said he had trust on his decisions and intellect. Chanakya said he would be a very humble master to him (meaning Chandragupta would rarely defy Chanakya's decisions).
Source- Parishisth Parvan
When Chandragupta and Chanakya were in hiding, they heard a lady scolding her child for eating hot food from the middle of the plate and burning his hand and thus being a fool like Chanakya. He should eat food from sides and then get to the middle.
Realising their folly, they decided to again attack Patliputra but first win the surrounding areas and encircle Patliputra.
They went to meet Parvatak, a King of the hills and with alliance with him they attacked the Nandas and finally the Nanda King was defeated.
Chandragupta and Nanda Princess
In Mahavansh Tika, it's written that Nanda King was killed and no mention of any marriage of Chandragupta with Nanda Princess but in Parishisth Parvan it's written that when Nanda asked for mercy, Chanakya allowed him to take his essentials which his one chariot could hold. He took two wives, a daughter and loads of treasure and left. When they were on the road, the Nanda Princess saw Chandragupta approaching (along with his allies and army) and she was instantly filled with affection and stopped blinking and stared at him like a goddess. With her side glances, she offered pleasure of future union to Chandragupta. Funny thing is Chandragupta was entirely oblivious of her staring and glances and didn't even notice Nanda’s wives and the princess.
Nanda realising he can't protect his family anymore told her to choose her husband as Swayamvar is a good option for daughter of warriors. (He basically told her to choose as Chandragupta was with his allies who were also Kings).
Hearing the words, she immediately got down from the chariot and ran to Chandragupta’s chariot. As soon as she put her foot on his chariot, nine spokes of a wheel broke, he said, who's this woman of ill omen wishes to climb my chariot? He stopped her but chanakya told him to not think otherwise as it was a fortunate omen and meant his descendants will get prosperity for nine generations. It's hinted he accepted her as his wife.
Parvatak and Vishkanya
Chandragupta and Parvataka entered Suganga Prasad (name of palace of Patliputra as mentioned in Mudrarakshasa) and they started sharing the booty. Now there is a story of Parvatak getting poisoned by a Vishkanya in Parishisth Parvan and Mudrarakshasa.
In Mudrarakshasa, she was a poison assassin sent by Amatya Rakshasa to kill Chandragupta but Chankaya gave her to Parvatak instead. As soon as he came into intimate contact with her, he died and it's hinted that the assasin was captured.
In Parishisth Parvan, she was brought up since childhood by Nanda King and she was trasured by the king and kept in heavy security.
Parvatak fell so hardly in love that he started seeing her as a goddess and gave a place in his heart. When they were on wedding mandap, they touched the hands, the poisoned sweat from her hands made him sick and he asked for physicians.
Chanakya told Chandragupta to ignore his plight and let the disease gets cured by itself because a king who does not annihilate a friend who wants half his kingdom eventually loses everything. And thus, Parvatak was assassinated.
Chandragupta and Durdhara
Chandragupta reunited with his family and married a daughter of his eldest maternal uncle who had came to Patliputra with the King’s mother. He wedded his maternal uncle's daughter and raised her to the rank of Chief Queen (Agramahishi).
It's not written but it might be a way to keep power within the family and get a queen who would not easily betray him.
Source- Mahavansh Tika
The name of his Queen is Durdhara in Parishisth Parvan.
In both the sources, when she was pregnant, she sat to dine with the emperor due to intense affection for the King.
Chanakya used to poison the food of Chandragupta to make him immune of poison but the king didn't know that. As soon as she ate the food, she collapsed. Chanakya ran towards her saying in distress What have you done.
He performed Cesarion and saved the child. Due to a poisoned blood spot on his forehead the child was named Bindusara. In Mahavansh Tika, the baby was kept in bellies of freshly cut goats for seven days and due to blood spots of goat's blood he was named Bindusara.
Chandragupta's reaction on Durdhara’s death is not written but obviously he would have felt grief over losing his trusted queen who was genuinely deeply in love with him. It's not mentioned who was Chief Queen after Durdhara.
Chandragupta had many queens as mentioned in Parishisth Parvan and Mahavansh Tika.
Sandrocottus and Seleucid Princess
In 305 BCE, Seleucus after winning Bactria decided to infiltrate beyond Indus and gain territories as lands were very revenue rich and it would help him in Diadochi wars, also he was an expansionist. He might also had wanted to regain the lands liberated by Sandrocottus and punish him for ousting Greeks.
After few skirmishes , Seleucus and Sandrocottus came to an understanding (likely Seleucus lost the war) and he gave up lands of Kabul, Kandhar, Herat and Makran to Sandrocottus.
Strabo mentions they established Epigamia which means Intermarriage between states and Appian says they had Kedos which means a marriage contract.
It's possible that as Seleucus was the one giving up the lands, he was the one gave up one of his daughters or a beautiful close relative and few other concubines and slaves to Sandrocottus.
Megasthenes who lived with Sibyrtius in Arachosia was sent as diplomat at the court of Palibothra and he closely watched Sandrocottus and his army and wrote a book Indica in which he wrote Sandrocottus was a conscientious and hard working King and whole day he spent in the court listening to cases and problems of his people.
Death:
Parishisth Parvan says Chandragupta crowned Bindusara as a King when he became a youth and then simply died in Samadhi.
Mahavansh Tika says when Chandragupta died a Yaksha named Devagarbha entered his body and started behaving like the King but his habits of gluttony and harsh speech made chief priest think he was a Yaksha and not the king. He told this to Bindusara and he staged a fake fight between two warriors over the weapons if Chandragupta gifted to Bindusara. When Devagarbha in chandragupta’s body told him to bring weapons to him as he would recognise it , Bindusara cut him in half, purified the city and became the king.
Mahavansh Tika is older text than Parishisth Parvan.