Basically I'd like to hear what people feel about this situation and am I or my partner being unreasonable in what's going on - apologies if this turns out quite long.
My partner and his mum have always had a strained relationship - stems from what he tells me was quite an unhappy childhood in parts and most of his adulthood as she was a heavy drinker and a narcissist (been sober years now). I've only known her since she hasn't drunk so I can only imagine, but could see how their relationship wasn't 'normal'.
Anyway I encouraged him to build bridges early on in our relationship and fast forward a few years, the relationship was still strained (lived away so didn't have many interactions with her) but we moved in with her to save money to buy a house of her own. In hindsight it wasn't a good move. It was a very stressful time for everyone but basically I saw another side to her which was manipulative and bullying (think ringing us whenever we left the house, partner worked from the house and she'd often barge in on him while he was on a call to demand various jobs were done). We moved out into a place of our own as soon as we could.
She and her husband (my partner's dad) were living separately and gaining grounds for divorce but it all stalled when he sadly discovered he had incurable cancer. He had a good job all his life and wanted to make sure his children and my partner's mum were all set up and to avoid paying a shedload of inheritance tax he left the bulk of his estate on paper to partner's mum but wrote a letter of intent alongside his will which outlined his wishes for more of the estate to be shared between the children to be invested wisely (think property). Partner's mum took him back into the family home and they made their peace, and where he passed away a lot sooner than we all expected.
Fast forward over a year since his death, partner's mum claims to have never discussed letter of intent with anyone, even going as far to say she was completely unaware of it (either a lie or genuine forgetfulness as she has poor memory) long story short she's claiming that his dad wanted her to have the remaining estate. Partner is understandably not impressed but in heated exchanges that have followed he's said he wants to go no contact, including not letting her see grandchildren. He can't believe she's stealing the dad's legacy which he wanted to share with his children to make sure they were set up. It's basically the final nail in the coffin of what was already a strained and difficult relationship.
This no contact is conflicting for me - he asked for my support in what is a very stressful and difficult decision to make which I did as I knew it was going to cause a big fallout. ( been nearly 3 months now) he reminds me that she is quite poisonous and doesn't want anything to do with her, she's stolen off the children ultimately etc. I've tried to encourage some family therapy, reminded him that the children are only young once, this will have further implications down the line at family do's that we wont go to if she is there etc. He is flatly refusing it as she has refused family mediation and is basically standing firm on the inheritance and he is standing firm on no contact as she is a difficult woman to be around (narcissistic) (and he has had a lifetime of knowing her and doesnt want her in his life anymore which extends to the grandchildren. She contacted me And said I've been part of the cruel decision and she's gutted but can see that the children are happy and looked after so that's the main thing,
Has anyone been in similar position and WWYD? am I doing the right thing in supporting him in this decision? 3 y/o mentions her occasionally (she was spending a day a week with her before the fallout) but partner wants no more mention of her name in the house. It's all so difficult and am seriously considering moving us all away so at least I've got some family support around us. Thanks for reading this far!
(apologies for typos, typing 1 handed while bf-ing baby and 3 y/o wanting my attention 
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