https://judyrodman.com/mechanical-licenses-for-recording/ This paragraph seems to cover your question, Donna. But I'm not a lawyer. Good luck!

Do I have to do a mechanical license with my own co-writers?
YES you absolutely do! If you, as artist, release a song publically that you co-wrote with someone else, you (or your label) must legally process a mechanical license with every one of your cowriter’s publishing companies, and again, do it before it’s publically released. Yes, you get your split. If you have 2 co-writers, they split 2/3rds of the total mechanicals.

Best, John