My father has four wives. However, he has ceased to have any conjugal relationship with his wives for many years now and has not divorced them. However, he now has new "wives" that he has not made their marriage public. These wives now have some children for him. My question is, as one of the children from my father's legitimate wives, how should I treat the other 'children'? Islamically speaking, are they my brothers? How should my sisters (those wearing hijaab) behave in front of them?