If they were the result of adultery, no they are not. Your mahrams are only his legitimate sons.

My exhusband abussed many woman(I wound out later on) and he has a lot of children from diffrent woman are all his children my Maharams?

Illegitimate children & Lost property | February 27, 2014 10:58 am
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My parents have property. from our gr. parents. this is actually a dowry my father got from my gr. father.now father decide share this property among us. but we know this property is dowry.so can we accept this.my fhtr share this property acording 2islam
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I’m a new Muslim, and I was wondering where does Islam stand on adoption? Is it haram? Thank you for your time.