Re: calling MIL's/SIL's/BIL's
My hubby calls his mother "Mum" which is different from what I call mine ("Ammi"), so it wouldn't have been weird for me. But he finds it weird, so I call her what I've always called her.
I call BIL (older) and SIL (younger) by their first names, because I knew them before we were married. If I hadn't, I'd probably add "bhai" to the end of BIL's name.