I like Sprint and would like to stay, but I don't want to sign up for a new contract by myself and then run into issues trying to switch onto my families family plan. I would also like to keep my phone number. My number would be the third line on an Everything Data Family plan.
When your contract is up, go in to the sprint store with the account holder of the family plan you are joining. They can add a line to the family plan and port your number over, which will close your old account in the process. If you plan on upgrading your phone wait until you are on the new account, as in when you are at the store doing the account shuffling and not when you are still on your own account.
Hello paleozoic, you will not have to worry about changing from a stand alone plan to a shared plan later if you were to renew your agreement now. The only concern you may face is wether, or not all three phones are on the account.