You do need a VIN to be a member. There’s a “Test Drive” membership for non-Porsche owners but it’s not a full membership and doesn’t even associate you with the region.
I can definitively answer the second question. He’ll be more than welcome to bring his BMW to IDS if he’s a member.
Are you actually using your associate membership fro a spouse or anything? If not, set him up as your associate member and you’re good to go.