My Paul died 7 months ago and I’m finding harder every day. He died of an aggressive cancer and, unfortunately, we didn’t complete his will in time (we’re not married). My mother in law didn’t want anything to do with sorting his estate out so left it to me do so. However as she was his legal next of kin I had to get a solicitor involved, as was her wishes. However Paul had life insurance to cover our mortgage and, unfortunately, his mother having found out the amount (even though she was told it was for the mortgage) stole half the amount, leaving me unable to pay the mortgage off. She states it’s so someone can take her shopping! Since then she basically told me to P off and hasn’t spoken to me since. She fell out with Paul’s sister 6 years ago but Iast Saturday they suddenly have started speaking to each other. (This is since the mother has grabbed the money). I’ve also found out the niece has spent £6000 of it in a week of having the money. I’m so upset and hurt as it is totally against Paul’s wishes and there’s nothing I can do. There’s not a modicum of grief shown. His mother hasn’t even been to the grave. All they want is his money. It’s tearing me in half that there’s been no grief. I’m unsure whether to contact his mother as she’s a connection to Paul or just forget about it. That’s if she will talk to me. It’s making me so very ill.
It can get ugly when money is involved. It’s also heartbreaking when you feel you are grieving alone without support. I hope you find some type of peace w/ it all.
I feel your pain 
My partner passed two months ago aged 43 and we weren’t married either. He didn’t have insurance or a will. He died within 7 weeks of diagnosis so we didn’t get chance to sort anything. We have a child together.
His family have taken everything money wise, they’ve been into the house taken every little bit of paper work they could find and his car. They’ve been through all our things, including my jewelry box. They’ve taken anything with money value, nothing with sentimental value!! This has hurt me alot as my partner trusted them to include me and protect me like he did. Families do stupid things when they are grieving. It’s heartbreaking. I’m sorry your going through this.
Oh no that doesn’t sound ideal, people can be selfish and it sounds like your mother is law is behaving in quite a selfish way. Did she have any relationship with him? It might be worth thinking about writing to her? explaining that he wanted the money to pay your joint mortgage , if you are feeling able to do that, but honestly, she is unlikely to give anything back, you will likely be writing for yourself, to let her know? At least you will have had your say that way,
If you can get legal representation, that might help you.
When my wife died, there was unfinished business. Someone Really hurt me and I spent (wasted) a huge amount of time playing it over and over in my mind, with my anger telling me to:
Go and deck them
They’ve got to know how much I hate them
Etc
Of course, I actually did nothing other than beat myself up regularly and made myself ill.
But! I started practicing mindfulness, and in there I learned a technique to resolve this sort of thing. It’s called a u turn, and Tara Brach is a great tutor on it. https://youtu.be/2m1pa_8MBb0?si=q2G0PGChUhxx2g8F
I very quickly moved on and never think about it any more.