My brother is going to get a share everything+ plan with 30 gigs data and he wants to add me onto the plan, but Im already on a 2 year contract. So is it possible for him to add me as an extra line even if Im still on my contract, or do I have to terminate my contract so he can add me?
Yes you would be able to move to your brothers account You would need to perform whats referred to as a "Transfer of Responsibility" since the account you are moving to is under your brothers name.
Depending on your device, you would be placed on an "Additional Line - Premium Tab" or "Additional Line - Smart Tab" pricing option.
Visit our pricing page here for more info