Cathy, I think this amounts to two choices.

Either comply, but ONLY if the inlaws pay 50% of the costs.
Or
You pay…but then you have 100% say.
Let the in laws decide. That way you are out of the clinch.

I know it's hard if your husband is so angry about this too. You are
sandwiched in the middle. Just lay these alternatives on the table,
and don't allow yourself to get pulled into any discussions.

Keep us posted!