After Ohema and Queenie helped their mother get inside Klaus's pants, and Miriam also helped her sister Tifa become Klaus's wife, the rest of the ladies came to the conclusion that, with how huge the paragon harem is becoming, they might as well expand it with people they know and trust.
Of course, a part of why they came to this conclusion had to do with something one of Chaos' wives who came to their aid during the awakening said.
Selene, being shameless, said, and I quote, "Everything good must stay in the family."
Nadia knew she had no one aside from her mother. The woman had practically spent her entire life making sure she was happy.
In fact, she hasn't spent an intimate moment in years. Maybe she personally did some self-touching every now and then to satisfy herself. However, for the past 38 years, after giving birth to Nadia, she never had sex.
So Nadia, seeing how happy Lunara and her twin daughters are with the same man, wanted the same.
