I’m looking for some different opinions because I don’t know what to do for the best.
Backstory - I got on reasonably well with my parents for most of my life. There’s been issues over the years as my mum can be quite controlling and makes everything about her, but family is family isn’t it and I always just got over it. But in the past year there’s been massive changes in my immediate family. My brother and his wife split up (he had an affair) and my parents (mainly my mum, but dad didn’t do anything to stop it) have treated my sil awfully. For example telling all the extended family how awful she was to my brother and how her family are being horrible to him now (understandly imo, he’s left her to bring up their kids and hasn’t seen them in months or given any money for them).
My mum kept trying to tell me all this too and I said I don’t want to get involved and tried to keep out of it while still seeing sil and kids. Basically my mum is livid that she can’t control me now and has sent some horrible messages about how I’ve never been there for her etc. There’s obviously a lot more to it than that, but I’ll be here all day..
So we haven’t seen her since Christmas Day (apart from a funeral mid January when she all but ignored me) They haven’t seen my 4 month old baby since Christmas Day. Not even a text to see how baby is since Christmas. They live less than half an hour away..
Current dilemma - me and DP have decided to get married in a couple of months. We were engaged before all this so they know that, but the wedding date was never set. We feel we can’t have the big wedding we intended as I can’t have brother and sil there without drama and it would cause too much trouble when I chose to invite sil. So we decided to elope. But it’s now evolved from that to inviting my best friend (to be witness) and her husband, and DP wants his brother as witness so him and his wife are coming. DP has very small family (literally brother and parents, so we said if his parents want to come too they can and we will all go registry office then get food afterwards. It’s not a big wedding.
But I don’t feel I want my parents there, and my DP definitely doesn’t. He’s so upset and angry by how they have treated me and that they don’t seem to care about our baby. And for how they are treating sil, though I appreciate that’s not entirely our business, but it does taint your opinion of people.
My mum has always said to run away and get married and tell people when we are back, so I don’t think they would be upset particularly about that, but they would be upset to find out my DP parents were there I think.
If I don’t invite them then that’s cemented that our relationship is over (which I think it pretty much is anyway) but it’s on me then, and the way they treated me is forgotten because I’m the one who left them out of my wedding. This is going to “prove” that it was me all along and how sad for them to have such a hurtful daughter, when in reality they have hurt me so much and me backing away is a direct consequence of that.
As it stands at the moment, I can’t tell one of my oldest friends (same friendship group as friend who is being witness) because her mum is friends with my mum and I don’t want it getting back to my parents like that. But I obviously don’t want to lose my friend keeping such a massive secret and basically leaving her out. But at the same time she won’t understand why I haven’t told them, and she thinks I’m over-reacting to how they have been. She thinks my mum is lovely 
What do I do? Does anybody have any advice? I want to talk about my wedding and I want to get excited over it. It feels like a big dirty secret at the moment, which it absolutely isn’t.