I'm not going to let my brother-in-law go on vacation with us. I think my husband won't like it.
Why won't you let your brother-in-law go on vacation with you?
He behaves like a child.
You shouldn't exclude your family members. Maybe you can set some boundaries with him so during the trip you'll spend limited time together.
It's my decision who I take with me on vacation.
It's also your husband's vacation too. Maybe he wants his brother along.