reply to Seems_t
Re: Can I combine accounts? You can't "merge" accounts, which is what you're wanting to do. That new phone is tied to a new account and you'd have to break the contract with Best Buy, which will come with ETFs.
You could potentially get the new account at BB then move your wife and son's phones to that account. zeddlar points out the issue with phone numbers (though I wonder if that can be handled).