I have not been on either side of this issue, but I would like to raise another side.
Let’s say that you have a child who wants to be married by a shinto priest in a traditional ceremony in a Japanese temple. Now, as a Catholic, or even a Christian, you object to it. WHen push comes to shove, you decide that, as a point you will not attend. Will your child be hurt? Yes. Will this cause damage to the relationship? Yes. Can the burned bridges be rebuilt? Yes, but it does not always happen.
Now, same thing, but you decide to go, so as not to upset the relationship. Are you doing something that is against your consceince and faith? Yes. It is a sin? Probably. Is it the easy way? Yes.
This is different from the situation presented. You have the option of going or not going. The OP’s situation is one where someone else is telling you that you are not worthy. I would find offense at that.
Now, is it possible that these people did not know until it is too late? Yes. It may not be intentional, but sometimes people do not know all of the information when they commit.
My prayers for all the families involved.