Your example is unambiguously plural. It’s not a good illustration of “they” creating confusion.
It’s truly not a problem. I could contrive a reason to talk about a couple (they plural) and a nonbinary person (they singular) and end up with sentences where you don’t know which I’m referring to, but the exact same issue happens if I’m telling a story about two “he” or “she” subjects. And it’s solved in the same way.
Person 1: Is your friend Bob coming over? Person 2: No, they can’t make it, they’re busy
One Bob, and we all know it’s one Bob, no confusion. Look for context. It’s not that hard.
Person 1: Are Bob and Janice coming over? Person 2: They can’t make it.
Sometimes additional context is needed.
Your example is unambiguously plural. It’s not a good illustration of “they” creating confusion.
It’s truly not a problem. I could contrive a reason to talk about a couple (they plural) and a nonbinary person (they singular) and end up with sentences where you don’t know which I’m referring to, but the exact same issue happens if I’m telling a story about two “he” or “she” subjects. And it’s solved in the same way.
Person 1: Are Bob and Janice coming over? Person 2: They can’t make it.
Alternative:
Person 1: Are Alice and Janice coming over? Person 2: She can’t make it.
Alternative:
Person 1: Are Alice and Janice coming over? Person 2: Alice can’t make it.
This is far less difficult than you’re trying to force it to be.