Yes, serve all parties if you can, however serving the occupant (I think) is OK. And assuming you used a lease that reverts to month to month after 1 year, yes, it still stands.
Personally I require tenatns to sign a modification addendum to the original lease if they go to month to month.
I don't like mtm, but in this market I'm having to do it. Tenants are concerned about being locked in for a year if their jobs go south (no pun intended) so mtm seems to take that stress off, and they stay anyway.
Sugested reading - the AZ LL Tenant Act.
--76.87.xx.xx