Returning the mahr back to the wife after divorce

Q: I wish to ask regarding the divorce. One of my friends divorced 3 years back and hooked up with another woman. His first wife was not a good woman. While she was with my friend she was keeping an affair with another guy. My friend got to know this and he divorced her and her parents gave back all the gold and mahr money as well but he is not aware. He would like to know should he return the mahr money or not?

Women driving

Q: I need advice. My father in-law has arranged for my wife and his other 2 daughters to go for there drivers licence, Masha Allah. Should he have asked for my permission to proceed with this arrangement, or he has the right to do this without my consent, and further more he arranged that my wife must come to his home in order to go for her lessons, and the mum will fetch her from my place and bring her back. I'm I wrong in questioning my wife, as to why she can't be picked up from my place instead, as I would like to know with who she's going.

Joining the British army

Q: My question is that I am thinking of joining the British army as a officer not really a soldier. What does Islam say about a Muslim joining a non-muslim military force? Also what can I do and cant I do? For a example a war against a Muslim country does Islam allow me to still fight against them? Also spying etc on Muslims is that haram?

Inheritance

Q: A Muslim father passed away and left his house to two daughters, [from previous marriage... mother is also deceased] and new step mom. What is the share holding according inheritance between the step mom and the two daughters?