Why can't my husband and I call each other on our iPhones?

We're not blocked, not in do not disturb, yes in favorites. It used to be I couldn't call him (when we had Verizon and our old 13 Pro phones). Now we have AT&T and 16 Pro phones and we can't call each other. If I'm looking at the phone, I might see that he's calling. Same for him. Our numbers are one off from each other. Does Apple think they're the same number? I don't want to add him to "emergency" (like I have my kids) since what to buy at Trader Joe's isn't an emergency. What is the solution? It's annoying to have to tell my kids to call him or to call his office landline for similarly time sensitive-but-not-emergency types of questions. Thank you.

[Re-Titled by Moderator]