Its not about who has the right, its about doing whats right...
PSquared, I hope both you and your husband's family will be happy with whatever you decide to do
and I don't think it's right for anyone to force their choice on someone else.
The in laws have the right to not participate in any function. But they don't have the right to forbid the other side in from participating in anything on their own. especially when it's not their money or time at stake here.