What is the ruling on marrying for Tahleel?

Is it permissible for a woman to stay permanently at her sister`s husband`s house, given that he is seventy three years old and his wife is forty five?

Is my wife`s stepmother forbidden for me in marriage forever?

Is it permissible for a father to give his daughter away (Marriage) to his uncle (Maternal)?

Is it permissible to join together in marriage a woman and her paternal aunt or maternal aunt, and what is the evidence on this?

My maternal aunt`s son and I are planning to get married. However, I found out that he was breast-fed by my grandmother for one time, but it wasn`t filling, as she pointed out, because she was in her late forties when she gave birth to my aunt, so she didn`t have enough milk. What is the Islamic ruling on this?