Carrier Adding more lines to my account

I'd go to a store to accomplish this, just so you can correct any issues that may arise. But if the CSRs are half-way compentant it should't be an issue.

You can also accomplish it online.

Just add two new lines. That will give you temporary phone numbers. When your parents are ready they port their numbers to those lines.

It's easier to do in-store though because they will have SIM cards they can give your right there. If you add two lines online then you have to wait for the SIMs to arrive.

If you go in store you won't need to add two temporary lines, you can just tell them you want to port your parents lines to your account. They'll need your account info of course.

You will be charged $25 per SIM (T-Mob's activation fee).

 

Go to Tmobile and they will answer all your questions.
They can mail them new sim cards or arrange for them to go to a local Tmobile store near them to pick up their new sims instead.