Yep above might be the best way. He is family by marriage but it may go smoother if your husband joined first. Think you can do it all on the same day. I signed up over the phone but If there is a local branch go in.
I'm interested in joining nfcu through my husband's grandfather (he has passed away but from what I've read we should still be eligible to join). Does my husband have to join first, and then once he's a member I can join through him? Or is there a way we can join together like a joint membership? We're mainly interested in the checking/savings at the moment but will be applying for credit down the line.
Once he becomes a member you will be able to join online by just entering his name, date of birth, and relationship that you have with the existing member.
NFCU has an active security department. You don't want to apply first because you do not have a direct relationship with the service member. There are many stories about individuals who have joined without proof of eligibility to later have their accounts frozen. Let your DH join first, it only cost $5 for a share savings account, then you can apply afterward.