No, Krishna, Balarama, Pradyumna, and Aniruddha are different. Lord Vishnu has four forms, namely Vaasudeva, Sankarshana, Pradyumna, and Aniruddha. These four roopas are responsible for providing Moksha to the people eligible for salvation and for the destruction of the universe, the creation of the universe, and the sustenance of the universe, respectively.
Out of the four forms of Lord Vishnu, Vaasudeva roopa incarnated as Krishna. Whereas Balarama has the avesha of Sankarshana roopi Paramatma. But He is the avatar of Aadi Shesha. SriMadhvacharya in the Bhaagavata Tatparya Nirnaya, clearly states आवेशे बलभद्रे, which means Balarama had the avesha of Sankarshana-roopi Narayana in him.
This Balarama was Lakshmana in the Ramayana, and there too he had the avesha of Lord Sankarshana, and is the incarnation of Aadishesha. Whereas if you talk about Pradyumna and Aniruddha from the Vyuha roopas, then yes, they are the same as Krishna and are non-different from Krishna, because they are His roopas only.
But if you mean Pradyumna and Aniruddha, Krishna's son and grandson, then they are not the same as Krishna. Because Pradyumna is the avatar of Kaamadeva and is the presiding deity of Lord Vishnu’s Sudarshana Chakra, plus, Pradyumna has the avesha of Pradyumna-roopi Narayana, of the Chaturvyuha roopa within him. In addition to this, Pradyumna was born as Bharata in the Ramayana.
Talking about Aniruddha, the grandson of Krishna, he is the avatar of Aniruddha named Devata, who is the presiding deity of Lord Vishnu’s Shankha. This Aniruddha has the avesha of Aniruddha-roopi Narayana, one of the Chaturvyuha roopas within him. This Aniruddha was born as Shatrughna in the Ramavatara.
Though it is Lakshmidevi who is primarily the presiding deity for the Vishnu Chakra and Vishnu Shankha. Lakshmidevi has three forms, namely Sri, Bhu, and Durga. In the Sri form, She is the presiding deity for the Sattva Guna. In the form of Bhu, She is the presiding deity for the Rajoguna. And as Durgadevi, She is the presiding deity for the Tamoguna.
For Bhagavan’s Chakra, Durgadevi is the presiding deity. For Bhagavan’s Shankha, Sridevi is the presiding deity. For Bhagavan’s Padma, Bhudevi is the presiding deity. Kaamadeva and Aniruddha too are the presiding deities for the Chakra and Shankha, but are secondary presiding deities. Lakshmidevi as Durgadevi and Sridevi are the primary presiding deities for the Shankha and Chakra. These presiding deities are known as Abhimaani Devatas.
So, in a nutshell, Krishna and the Chaturvyuha Moortis, namely Vaasudeva, Sankarshana, Pradyumna, Aniruddha, and Lord Narayana, are the same and have no difference. There is no hierarchy, no superiority or inferiority among these roopas and Krishna. All are the same in terms of strength, intellect, mood, valor, beauty, etc., and are flawless. So, Krishna is Saakshaat Vaasudeva roopi Paramatma.
[Sriramana, Bhuramana Durgaramana Govinda]
Whereas in the case of Balarama, he has the avesha of Lord Sankarshana and is the incarnation of Lord Aadishesha. Talking about Pradyumna, the son of Krishna, he has the avesha of Pradyumna-roopi Paramatma and is Kaamadeva’s incarnation. Whereas in the case of Aniruddha, the grandson of Krishna, he has the avesha of Aniruddha-roopi Paramatma and is the incarnation of Aniruddha named Devata.
Jay SriRam!
ShriKrishnarpanamastu!