If they are not his kids, he cannot get custody of them. Is he on the birth certificate? If he is, the answer may be different.
Michael is in San Jose, California and can be reached at 408-295-4232 or at firstname.lastname@example.org. Consultation fees, rates and retainers vary based on need and ability to pay.
If you are married when the current child is born it will be presumed a child of the marriage. yes, that could result in his having custody if you divorce after the child is 2 years old.
Why are you marrying when you seem to prefer a non monogamous lifestyle...? What do you suppose are the odds a marriage based on a lack of candor about such a basic issue as this will work out?
I promise you the divorce will be costly-- good for NO ONE.