I think its less about the models and more about the opportunity. Its rare to have two avns like that and avn's usually lack cool male characters so the logical "cool" solution would be for one MC to be the son of the one you played before and being part of the legacy "you" started to build in wiab again.
And imo wasting this is a missed opportunity. Nika just being the son of some rando unrelated to the wiab plot would be a huge disappointment and boring.
The only other option i would consider equally satisfying would be for Nika to be the son of the villain/antagonist in wiab who maybe got killed by William. But we would need a really cool wiab antagonist for that.
Just keeping Nika and Nami in a parentless limbo would be my least favored choice, could have just given him a real family in this case or at least memorys and picture of his parents and him remembering them and their teachings (for emotions, immersion and so on). But remembering stuff isnt Nika's strong suit anyway i guess