I have been researching on this topic for a very long time. However, I did not find any conclusive answers yet.
Kayasthas are believed to be descendants of Shri Chitragupta, who is 17th child of Brahma, born from his mind and soul. However, no information gives a valid answer as to which varna does the Kayasthas belong to. So, a Brahmin boy of Srivatsa Gothra marrying a girl belonging to Kayastha community of Kashyapa Gotra, is it valid.?
What is invalid in that?
If you were researching on the varna that Kayasthas belong to, the below excerpt from a lecture of Swami Vivekananda (a Kayastha) might help you : -
"One word more: I read in the organ of the social reformers that I am called a Shudra and am challenged as to what right a Shudra has to become a Sannyasin. To which I reply: I trace my descent to one at whose feet every Brahmin lays flowers when he utters the words — यमाय धर्मराजाय चित्रगुप्ताय वै नमः — and whose descendants are the purest of Kshatriyas. If you believe in your mythology or your Paurânika scriptures, let these so-called reformers know that my caste, apart from other services in the past, ruled half of India for centuries. If my caste is left out of consideration, what will there be left of the present-day civilisation of India? In Bengal alone, my blood has furnished them with their greatest philosopher, the greatest poet, the greatest historian, the greatest archaeologist, the greatest religious preacher; my blood has furnished India with the greatest of her modern scientists. These detractors ought to have known a little of our own history, and to have studied our three castes, and learnt that the Brahmin, the Kshatriya, and the Vaishya have equal right to be Sannyasins: the Traivarnikas have equal right to the Vedas. This is only by the way. I just refer to this, but I am not at all hurt if they call me a Shudra. It will be a little reparation for the tyranny of my ancestors over the poor. If I am a Pariah, I will be all the more glad, for I am the disciple of a man, who — the Brahmin of Brahmins — wanted to cleanse the house of a Pariah. Of course the Pariah would not allow him; how could he let this Brahmin Sannyasin come and cleanse his house! And this man woke up in the dead of night, entered surreptitiously the house of this Pariah, cleansed his latrine, and with his long hair wiped the place, and that he did day after day in order that he might make himself the servant of all. I bear the feet of that man on my head; he is my hero; that hero's life I will try to imitate. By being the servant of all, a Hindu seeks to uplift himself. That is how the Hindus should uplift the masses, and not by looking for any foreign influence. Twenty years of occidental civilisation brings to my mind the illustration of the man who wants to starve his own friend in a foreign land, simply because this friend is popular, simply because he thinks that this man stands in the way of his making money. And the other is the illustration of what genuine, orthodox Hinduism itself will do at home. Let any one of our reformers bring out that life, ready to serve even a Pariah, and then I will sit at his feet and learn, and not before that. One ounce of practice is worth twenty thousand tons of big talk. "
https://en.wikisource.org/wiki/The_...es_from_Colombo_to_Almora/My_Plan_of_Campaign
