Apologies as this may be long. My mum has been with her partner for just shy of 20 years, prior to this he was married to another woman who he had named on his will as the sole beneficiary. When they broke up he changed it to say that his 2 nieces will receive everything. He married my mum 2 years ago but refuses to change it again (despite having changed it 4 years ago when his niece had a child). So currently my mum would receive his pension and a small amount of any life insurance. That in itself would not be such a big deal except that he is telling my mum that the only reason he isn't changing it is that now he is married his will is no longer enforceable and she will.get everything.
There is a huge backstory with it all, he refused to live with her until we had all moved away so they have only been living together for about 5 years. He made my mum sell he house because his uncle died and he inherited enough to pay off his mortgage. He was then made redundant and has not looked for work since (he is in his early fifties). Despite having no mortgage to pay he makes my mum pay him £600 and when she questioned this he said that he needs it because his redundancy money has nearly run out and she would pay more if she rented somewhere 
but he won't put her on the deeds either. So even though she is paying him this money (she also pays for all of the food, drinks, travel, holidays etc) he has made sure she won't get the house and says it's fine because she can live in it as long as she likes or sell it to buy somewhere bigger and then his nieces will get that house instead.
My mum was upset when she spoke to me and said she thinks he is trying to make sure that me, my brother and sister won't get any of his money. I understand that and wouldn't want any of his money but my mum could have bought her own house instead of paying for him for 5 bloody years. She feels like it's not an even partnership and that it shows he doesn't think much of her.
He has had his issued with us, he banned my sister from his house so she couldn't even come for Christmas because he doenst like her partner (her partner came round to his with wine and chocolates to try and speak to him but he wouldn't even go to the door). Last year I had my son and a few weeks later lost my partner, I then found out my landlord was selling the house and when I managed to find somewhere new I needed a guarantor due to being on maternity leave. My mum instantly volunteered (I have a well paid job and have never had issues with money or debt so she knew there was no chance it would be an issue). I was on the phone to her and he came in shouting at her, she thought she had hung up but I could hear him screaming at her "you stupid fucking woman, you never think anything true" and telling her I was untrustworthy (I have no idea what he has based this on)
Anyway there are a million things I could say on this subject and I've been worried about my mum for years. He is also an alcoholic which is why he can't work. I'm really looking for advice on what rights she has with regards to the Will (i.e. could she contest it as a spouse). She said to me today that she is thinking of moving out and I want to tell her I think she should but I don't know if my dislike of him is clouding my judgement, I don't want to be the one to tell her to leave if it will make her unhappy.