Does a husband and wife entering the store each need their card out or is one to show enough?

You are not required to have membership to purchase Rx from ANY pharmacy (or to purchase alcohol from any store). ;)

You can even take a friend, let them shop, and use your card on check out. Worst case say that one purchase is for personal and the other for business.

One is enough

One is enough :-) A lot of times they don't even ask to see the card when you go in, but you have to show it at checkout.