We have a Business membership but it only has one card with my husband's name. With my ID, with the same last name and address, can I use his Costco card?

You can also get a card and it will not cost you anything

It might be possible, def worth calling and asking instead of going and being denied at checkout... But more than likely you will have to be added on and get ur own card to use... Thats how the other memberships run, u have to add users to ur account and they get their own card... But def call and inquire

Yes, you should be ok. At least do it once and give you a warning.