Have had First Net through work for a few years now, can I add lines for my personal phone and family?

The hospital I work for used to pay for cellphone services/lines for work purposes through FirstNet, but they slowly started cutting back on that. At this point, I now pay for my FirstNet account and am trying to decide whether I can just add lines for my personal number and my family. I like having access to the FirstNet service because coverage is really great, but I can't find much info on how to add other lines/how that would even work. If the other lines are basic ATT lines, do you find that the service is as good as FirstNet?