What would it take for a lawyer to practice in multiple states?

I'm in the middle of a custody battle in which neither of us live in OK, which is where we were divorced and our legal battle began. He lives in CO, I live in NM. We've been bouncing back and forth between court in OK and NM. I've had to hire lawyers in both states but his lawyer out of OK but working in NM,too. How does this work?

Some states its very easy to receive a license in , if you are already licensed in another state.

But yes, lawyers can be licensed in more than one state.

Many lawyers have licenses in more than one state.