Bonbon
It is not your fault your mother is like this and you did not make her that way. Do read the book I recommended earlier, my guess is that she has always been difficult to get along with and you've had to placate her your entire life. Your mother has never apologised nor has accepted any responsibility for her actions.
Re this part of your comment:-
"So my husband and I used to fight quite a lot because I tried to keep my mums behaviour a secret... I don't know why, maybe embarrassment and maybe just family loyalty".
I am glad you no longer try and keep her behaviours towards you a secret; abuse thrives on secrecy. FOG (fear, obligation and guilt) keeps people feeling trapped as well.
re this part of your comment:-
"He also used to think his mother was a Saint and took her side all the time. Now that he sees her more he is realising how she is as well. I am opening up more and we try to laugh off lots of things they do to annoy us. They both have a day each during the week and then he goes to nursery the rest of the time. We both work. My mum is very jealous natured and envies the fact MIL is retired. I'm sure she thinks she's in our house 24/7 but she isn't I make sure of that. MIL is very controlling and has been very controlling previously in our lives but I am trying to take back some control and husband is helping with that. For example she used to come in, go upstairs and empty our washing basket.... My underwear is mine and mine alone to deal with.. So my husband told her that was a no no. She still makes a deal out of it sometimes... Oh I'm not allowed to do anything. MIL also thinks she can just take my son, the day after we came back from his first holiday abroad she said so will I just take him home to mine tonight? Erm... No he needs to get back into a routine. So I am getting stronger with MIL but I feel I can't be as strong with my own mother, she just cries and says oh well it's all my fault then. My brother and sister in law have tried talking to her as well but she can't see her behaviour is so wrong. I asked her to go and speak to someone about her mental health and she just said everyone is allowed to be down sometimes. There is something not right in her head which I guess is why I maybe let her away with so much. I just envy people who have normal parent relationships"
Unfortunately for your H, his mother is really just as disordered of thinking as your own mother. I would not be wanting her in your house either because controlling behaviour like she has shown you is abusive as well. What she wants as well as your mother is power and control over you both; this lies at the heart of abuse. Do not also let your mother get away with as much now; this is how she has taken advantage of you as her daughter. You have every right to assert yourself here as a woman in your own right.
Thankfully you are now both putting down far higher and consistently applied boundaries, this will certainly help you as he going forward particularly if you remain firm and consistent. His mother is all too adept as well at piling on the waterworks; tears can also be manipulative.
Your only mistake here has been for either your mother or his mother to be as involved in your lives as they have been. MIL should no longer have a key to your property; if she still does I would get the locks changed. These two women (and their own male enabler husbands for that matter) have to behave decently around you and your H and they both cannot or equally will not do this for their own reasons (none of which are to do with you or your H). I would not want either of them to be around any of you now, let alone your child.
Such people never apologise nor accept any responsibility for their actions; this is also why others talking to her has met with no success.