Yes - you can program multiple vehicles to one key card.
My key card is currently authorized for three vehicles - both of our Model 3s and our roommate’s Model Y. It’s great.
Treat your key cards like commercial access control cards - each person has their own card that gives them access to whichever vehicles they’re authorized to drive. This is much easier than family members digging through a drawer of cards to find the one they’re looking for.
Note that key cards can be - and phone keys are - named. When you go to Car Menu > Locks, you’ll see a list of people who have accessed the vehicle along with their most recent access date or time, along with the access method (card vs phone).
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