To add a dependent to tricare, do you have to physically go to a DEERS office?

It depends on whether you're on active duty status or retired. If you're active duty you don't need to update DEERS, but if you're retired and the child is 18 years old or older, yes. The child must be a full time student to get updated and a new card. Dependents under 18 are covered in Tricare until they reach the age of 18 and up to 22 years old as a fulltime student. My recommendation would be to update DEERS when the dependent is 18 years old with the proper documentation showing they are full time students. This information is based on my personal experience with my dependents and Tricare. The Tricare office will answer any questions you have regarding my experience with their office.

I don't know. I do know that if you contact the particular office by email or phone they should answer promptly.