In America, yes.
If you are related by blood, yes.
yes, and illegal in some/most countries
A brother can't marry a sister it's against the law, but you can marry your 2nd cousin and down.
If your brother-in-law's ex-wife is your sister, you cannot marry his ex-wife.If your brother-in-law is the brother of your wife, then as long as you are no longer married, you can marry his ex-wife.
No, it is not illegal.
No, it is illegal to marry your sister anywhere in the world.
A sister marrying her brother would be incest and there would be a substantially increased risk of birth defect or genetic disease in the children of such a marriage. in all societies currently existing on the planet it is illegal for a sister to marry her brother. not in all societies, but the rest is correct
no its not illegal
No. Incest is illegal in all countries and the risk for having damaged children is big.
yes you can marry because she is your cosin sister
You can if your brother and his wife break up. but you have to be a man though. brother and sister can not marry.
No. Your brother-in-law is going to be your brother-in-law as long as your sister stays married to him. The "title" is a customary one, not a legal one and will not change because he develops a second family relationship with you.
Where polygamy is illegal it is illegal to marry someone's husband. If this man is someone's husband, he is not permitted to marry anyone else.However, if your mother's sister (your aunt) is deceased you could marry her husband in most countries. He is not related to you by blood.