Q: Why did lord Krishna not marry Radha?
To understand Radha correctly you need to somewhat understand the mysteries of “rasa” and “prema” – the ecstatic experience of spiritual love. Krishna and Radharani playfully married once, as children sometimes do. They did not really marry, however, because their love is more primal, profound, and unbounded than what wedded love facilitates. Wedded love is a very elevated type of divine union with the Supreme Personality of Godhead, yet in marriage the intimacy and spontaneity is not limitless. Some limitation is imposed by the sense of “duty” that husband and wife naturally acquire towards one another. This sense of duty is beautiful, but the highest type of love is even more beautiful. It is so profound that it requires no sense of duty – and flows absolutely spontaneously – breaking all things that stand in its path. Thus the pure transcendental love that Radha and Krishna enjoy on the highest level of bliss (paramānanda) expresses itself in the form of being paramours, not being husband and wife.
Q: How many wives did Krishna have? What was the names of his wives? How many sons did Krishna have?
Krishna does not marry anyone or have any children.
However, Krishna’s first expansion, as the king of Mathura and Dvaraka does marry. This “Krishna” is slightly distinct from the original svayam-bhagavan Krishna, who never exits his Dhāma, Vṛndāvana. This first expansion of Krishna is known properly as Vāsudeva Krishna.
Vāsudeva Krishna first married Rukmini, and then married another seven goddesses, headed by Satyabhama. Jambavati is another prominent one of these original wives. A little while later, Vāsudeva rescued 16,100 ladies from their abduction into a harem, and then married them all. He personally lived with each of his 16,108 wives simultaneously.
We hear that he had 10 sons with each wife. I have seen lists of names for the sons only of the 8 original wives. The most famous are Pradyumna, Samba, etc. I am not sure if he also had many children with the thousands of other wives, nor am I sure how many daughters he had. When Vāsudeva Krishna departed from the earth, there was a terrible event that allowed almost every single one of his family members to leave the world at about the same time.
Q: Was Radha realy Krishna Aunti?
Radharani is the daughter of Vṛṣabhānu and Kīrtidā. Krishna is the son of Yaśodā and Nandā (Vāsudeva Krishna, a little different, is the son of Devakī and Vasudeva). There may be some distant relationship which would make Rādhā and Krishna some type of cousins, but if that is the case, I am not aware of it. So far as I know there is no family relationship between Rādhā and Krishna, and certainly Radharani is not Krishna’s aunt. That is rather preposterous.
We should mention that Krishna’s mother, Yaśodā has so much motherly affection for Sri Rādhā that she treats her exactly like her own daughter, you can say, exactly like her own “Daughter-in-law.”
Q: Why is Krishna blue in skin color?
Blue is a word that is moderately useful towards describing the transcendental color of the Supreme Personality Śrī Krishna. Here is a more elaborate and accurate description: imagine a mountain of dark-blue sapphire. It would be almost jet-black. Now imagine the sun rising behind that mountain. That is something to give a clearer idea of the color of Krishna. Very black, but with a blue brilliance.
If you understand how light produces color, it will make clear sense why Krishna is so black. Black is the color that attracts light absolutely, and no light bounces off a black object. Krishna is all-attractive. Therefore he is black, every energy is completely attracted to him and never departs from him.