All right, update: I opened the cards. Posting about it turned it from a little thing to a big thing, apparently - good call, @kindness. And as @Hedgehog said, no one was trying to stress me out with the cards.
One from my cousin, which included adorable baby and puppy pictures, one from a friend, and one from my dad, which is always emotionally fraught. But it’s done and everyone survived.
Thanks to everyone for your comments - I got a lot of insight into what’s going on in my head about this.