Jr baby name??? Help!

Jo

So me and my hubby have decided that if we have a boy we are going to name it after him. but here's the thing.. his name is Roy Garrett Gebhard, he took his mother's last name to continue on the Gebhard last name as he is the last male in the family & the name would end if he didn't take his mother's. His dad's last name is Barnum, which you may recognize from his great great great grandfather P.T. Barnum from the Barnum and Bailey circus! if we were to name our baby Roy Garrett Barnum-Gebhard would he still be able to be considered a Jr? not sure what the rules are for naming a Jr lol