Change of responsibility.

Me and my wife are on an old Tmobile one plan with my Mom. There are 8 devices total and i want to break away from her plan to be able to add devices in the future as my kids grow. Mom also wants to add a line but is told she cant unless she upgrades and 8 lines is the max on the one plan. So me breaking away to my own plan makes sense.

Currently our plan is very cheap. I know costs will go up but can I do a change of responsibilty for my lines only and go to the better value plan or do I not qualify? Plan is new and i am getting confusing feedback. I want the better value or eperience beyond but that one is 170+ fees for just 2 lines. Better value seems to be better value. Lol

A person at costco said that if i am coming from a different carrier then i might be able to go to the better value but i would have to leave for 90 days. Does anyone have suggestions on that? Or plans with no cancelation fees? Sounds like i cant just switch to better value...

Side note: we are an android/samsung group of people and the s26u is out now. I usually buy on samsung direct but since we are looking at plans i am open to suggestions on how to make this transition go further and get my wife an upgrade from s23u to s26u.