I have a theory Vanessa is a love product of Leia & WiAB MC
Hi! I have a similar theory, but sometimes I think Ocean is sending us on a red herring hunt with Vanessa. He knows that a lot of WIAB players play SG too and that we are searching for clues hinting at the "canon" ending he envisions for WIAB and "crossovers" in general.
Vanessa might be a bit too bold and obvious to be one of Willi and Leia´s children. I theorise the cousins Ayua spoke about are actually her halfsiblings. She said to learn some of their special martial arts moves you have to marry her or one of her cousins. While she could have spoken about Miru sister´s (if she still has a sister in new WIAB) children too, they are in Japan, so hardly available in a provincial city somewhere in America like Wollust.
So these cousins have to be there in the city and the children of those knowing this specific style. This leaves the kids of Leia and Kati as available cousins of Ayua. Kati is leaning more towards lesbian than hetero, so Leia´s kids are more probable.