Thank you for all your thoughts.
My DSIS and I were bridesmaids when my DF married DSM, it was lovely to be involved and my brothers did readings. DM wasn't there but she was at their much larger engagement party and it's all pretty amicable. She was pleased they involved us.
DP and I are recently engaged and have talked to the DSC hypothetically about the idea of us getting married. I've left it to him as want them to feel able to be completely open and they've had a few chats.
They've said they love me, want us to get married and want to be involved - walking us down the aisle, handing over rings etc. But they've also said their DM has told them we're not allowed to get married, Daddy's not allowed to marry anyone and she'll be very angry with them if they're there (should it happen, she doesn't know we're engaged).
They've been divorced ages, I'm not OW, she's been fine about them spending xmas with us and my family, we have them every weekend and in the week, she's happy for me to look after one while she's arranged stuff for DP to do with the other one (whole other thread). She's just pre-empted any talk of them being at our wedding should we marry by saying they'll upset her and she'll be angry.
What position does that put them in? And what do we do?
Of course we want them to be there, we've never been able to imagine doing it without them. I can't think of anything lovelier than us being together and it'll be a small do anyway, just a simple ceremony and a meal afterwards.
Do we risk letting them know when it's happening, them telling her and them being banned from attending? Doing it as "a surprise" and them being put through hell when she finds out they were there? Or risk them blaming us for excluding them, when it won't feel right doing it without them anyway?