In Valmiki Ramayana, Sumali the Ogre had a beautiful and illustratious daughter Kaikesi. Once he saw Vaishravan Kuvera going through his aerial car Pushpak. He wanted to do good of Ogres and he told Kaikesi to go to Vishrava and marry him. Kaikesi not realising it was inauspicious time went to the Ashram of Vishrava and he was meditating. She stood in front of him all coy and shy. When he opened his eyes he found Kaikesi there and asked about her visiting him. She introduced herself and then told him to know her intentions through his meditational power. He realised her intentions through his meditation and said their union would produce terrible and fierce children because they met at inauspicious hour. She was terrified and didn't wish to have such terrible children and then he told her that their last son would be very noble and dharmic. Vishrava and Kaikesi eventually had Dashgriva, Kumbhkarna, Shurpanakha and Vibhishana. Dashgriva was later renamed Ravana because he used to make the world cry.
Source: Valmiki Ramayana
The origins of Ravana and his siblings are entirely different in Mahabharata by Ved Vyas. In Ramopakhyan, Pulastya had a son Vaishravan with his wife Gau but Vaishravan served Brahma instead of Pulastya and this angered him and he made himself into half and Vishrava was emerged. Vaishravan was King of Lanka with the grace of Mahadev and was owner of Pushpak Vimana. Seeing his father Vishrava was angry on him, he gave three Rakshasa girls as gifts to him: Pushpotaka, Raka and Malini.
Pushpotaka gave birth to Ravana and Kumbhkarna, Raka gave birth to Shurpanakha and Khar and Malini gave birth to Vibhishan.
Source- Ramopakhyan, Mahabharata, Gita Press
The Lanka in Valmiki Ramayana was in the South of Vindhyas and in Indian Ocean and most likely today’s Sri Lanka. Ram Setu also known as Adam’s Bridge is one of the strongest archeological evidences of Ramayana.