"Carrie, I think most people see where you're coming from, not just Karma. Has anybody said anything different? The only difference us that almost everybody else has said you need tk continue putting your daughter'x needs first."
MsVestibule, this comment implies that I am suggesting the OP will not be putting her children first if she refuses to allow them to be bridesmaids.
My position on this is that she would not be allowing her children to be used by her ex and his new wife, as if they are accessories, rather than real children (with needs not being met by their father in the areas which truly matter). I disagree that the maintenance is a separate issue - it is very much an indicator of a person's attitude towards their dc and all other decisions that the RP makes, hinge on the attitude of the NRP towards those children.
There are people who think that a father's involvement is to be encouraged in all cases bar actual abuse. I disagree. I believe a good father's (or mother's) involvement is essential, but if a man is not a good and responsible father then it's maybe better to not go all out to keep him involved. My feeling is that a bad parent is more damaging than having no parent at all. I think that constantly covering for a bad parent, just prolongs the inevitable, because the kids end up learning the truth eventually.
I'm not suggesting that the OP bad mouth him, but equally, I don't believe that being a bridesmaid puts a child on the same footing as the new step sister. What would put the OP's children on the same footing, would be financial support form their dad, not wearing a pretty dress for one day.
I just think it's not appropriate to be bm in this particular circumstance, so unless the girls were desperate to do it (in which case the Op has little real choice), I would gently discourage it.
For all the people who believe the girls will hold it against their mother, I think it is equally likely in future years, that they will see it was inappropriate.