She is clearly getting very much ahead of herself...discussion of any proceeds from an estate and wishes stated in a will etc are only relevant after death. Personally I would say to SIL go ahead and let her mount up her legal costs..it is sad that mother is caught up in all of this but if she is being manipulated by SIL and can't for whatever reason recognise this or see her loving kind son as before unless you can speak privately ..write to her or ask a trusted family friend to mediate am not sure what you can do. I certainly wouldn't agree to her demands on her expected proceeds of mother's house and remind her until mother passes away it is an inappropriate discussion and in any case your OH will insist on 3 valuations of the peoperty and she will pay a fair market price when the time comes. She is bullying your OH...she has no authority to question FIL/OH bank ac or cash flow during that time I would tell her to take a running jump if me. I hope your solicitor will give you sound advice on this...and hopefully confirm legally to you she hasn't a leg to stand on.