Currently, I'm on a family plan with 3 total lines. I'd like to transfer an upgrade to my line, but the other two lines on the plan would like to switch carriers at the end of the contract. Can I use the upgrade now on my line and stay with Verizon another 2 years while the other lines can switch at the end of the current contract in a couple months? This is mainly an issue because I'd like a new phone since my current one is not working well anymore and I don't want to pay full price while I have an upgrade lying around.
Taking a lines upgrade is only taking that phone, not the line. So, to get that upgrade phone you have to upgrade that line. That line would then be under contract.
Yes, each line has it's own contract, it's just that you can add more phones and lines to a single account for less than you could doing each individually under an account for each.
So, the fact that the line I want to upgrade is part of a family plan is irrelevant?
You said you want to "transfer" an upgrade to your line - which implies that your line is currently NOT eligible to upgrade. You also stated that the other two lines want to leave at the end of "the" contract - are they currently eligible to upgrade?
Each of the three lines has it's own contract, contract end, and upgrade eligibility. IF you use one of the other two lines to upgrade your phone, the other line's contract will be extended, and they would then pay a hefty ETF to leave Verizon for another carrier.
If the other two lines are currently out of contract, and they want to leave, they can do so now without penalty. Your best bet is to find a good used phone, or borrow one from someone until your line becomes eligible to upgrade, or simply forget the upgrade and buy something from eBay or swappa,com and have no worries about a contract once yours expires.