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.
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.
The original makes sense. Both your alternatives are weird. The first is completely strange the second one begs the question, what about Janice.
What are you trying to express here?