If I live in a household with my in laws and I get car insurance do I have to add them onto my policy since we are all in the same residence - even if they are not going to drive my car?

If they have their own cars and insurance, no. If they have valid licenses but do not own cars then yes, because if they borrow a car (someone else's) and get injured the PIP is on your policy or have an at fault accident the liability can come back to you. All licensed operators in a household with car insurance must be on a policy (each can have their own cars and own insurance but if there is only one policy, they all must be drivers on that policy).
You can NOT exclude any drivers on your policy in NJ. It is not an option.