Is it weird to date your brothers wifes sister?
It's weird. He could potentially be your brother-in-law before he's your husband. If your sister begins dating a member of the same family you are, do everything in your power to end it, and avoid the struggles.
Can you marry your wife’s sister?
If a man has a widow, he's dead and can't marry anyone. If you mean a man is a widower (his wife has died) is it legal for him to marry one of his wife's sisters, then it is legal for him to marry his former sister in law in the United States.
Can you marry your ex sister in law?
Your ex sister-in-law, (or your brother's widow) is not a blood relative and as such, any place without religious-based restrictions will allow your marriage. If your wife has passed on or you're legally divorced from her, you can legally marry her sister (your former sister-in-law).
Is an ex wife still considered family?
Even after the legal dissolution and remarriage, ex-spouses who have children together will always be those children's parents. Parenting decisions have to be made, schools and extracurriculars have to be chosen, homework has to be monitored and transferred between houses.