I am assuming that this question is addressed to me, despite the arrows, since the previous post did not assert such a thing: I did.
FIrst, there was a rule among kshatriyas that there had to be 7 degrees of separation b/w groom and bride, so forget first cousins, but even sixth-degree separated cousins couldn't marry. Anyway, since Arjun married Subhadra, Krishna married Bhadra and Mitravindya, it's clear that this rule wasn't applicable to Yayati's descendants, for whatever reason.
However, there was also a rule that if a man belonging to family A married a woman belonging to family B, then after that, a man from family B couldn't take a woman from family A as his wife, since family B was considered 'subservient' to family A, and that couldn't be reversed by marriage. So, take the Ramayan. Sita's sisters could marry Rama's brothers, but had Sita had any brothers and had Rama had more sisters (other than Shanta), Sita's brother couldn't have married Rama's sister: that was against the rules.
Yet, the above discussion of Yudhisthir's daughter marrying Krishna's son violated that very rule: since Subhadra married Arjun, no son of Krishna could have married a daughter of a Pandava. However, any daughter of Krishna could have married another son of a Pandava.
But since suthanu did married bhanu and there are many texts including harivasma vayu puran to mention this fact so i think the rule was not applicable to yayati s descendants either