Hm not that simple though. Is being a father simply biology or more.
It seems he was with his wife when the kids were born and split up when the children were older. Only after his ex wanted more did he do a DNA test and found out the truth. If he had the suspicion earlier he should have got it done.
To the twins he is their dad. I don't deny the wife isn't a cow but you can't suddenly disown children like that. I'd set up a trust account have half the money to the wife and the other half into an account neither she nor the girls can touch till they are older.
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