Hopefully Not A Dumb Question...
You can play tPvP on the same team as your friend at any time. You can sPvP with your friends if you’re put on the same team, or if a space becomes available on the other side, and either of you switch teams during the fight. Most of the time in sPvP my wife and I end up on different teams in sPvP.
Really the only way is to do tournaments. You can submit a partial roster for free tournaments. Other than that you can hope you get on same team in spvp server.