Can I cancel a tmobile contract?

My family have two phones on a 2 year contract. We only use one phone and we want To get an iPhone from verizon instead. So is there some way to cancel the contract on one phone an stop paying for it?

Yep, 2 ways to do it.
First you can call customer care and explain that you need to cancel your line (Whichever you need to). But doing it this way will also cancel that number.

Second, you can go to verizon and request a number transfer or port and they can get that number (Phone number of the line to be canceled) from T-Mobile. Once Verizon ports that number over T-Mobile will automatically cancel that line and send you a final bill.

You would then want to call T-Mobile customer care and put the existing line on an individual plan so you are not paying extra when there's no need.