I've never played more than one team in a franchise before but I believe you can select as many teams as you want when you are at the team selection screen when you are setting up your franchise.

orangepower75_PSN
@orangepower75_PSN
Posts
-
-
In Franchise when moving from Spring Training to the regular season or from regular season to the playoffs, I've never understood why it doesn't have a pop up asking you to select your 26 man roster. This seems like it would be an easy fix to this problem. When everything is set to manual I expect to have total control over every roster move.
-
I'm pretty sure that MLB the show franchise has an unlimited amount of seasons. I think you can play forever if you'd like. As far as changing teams you would have to leave GM mode on when setting up your franchise. That allows you to change teams after the contract is finished.
Second franchise team
playoff roster
Franchise repeatable?