I'm not too sure the mixed teams are the best JTR composition. Whichever plug-and-play toons people put, they don't last. JTR is almost dead on my shard, and it's full of krakens.
If you're going for a full Resistance lineup, Holdo might be a great options. Some lineups I think might work are:
JTR, BB8, Holdo, Poe, R2 (the tanky, long battle variation - Poe and Holdo as double tanks, R2 and BB8 support, only damage source is JTR and exposes).
JTR, BB8, R2, Scav Rey/RT, Poe/Holdo(only one tank, but with one more damage dealer. Poe would probably work better with Scav Rey because he can provide buff immunity, and RT has an additional buff dispel so Holdo works).
JTR, BB8, Scav Rey, RT, Holdo (yes, no R2. Re gives a cleanse, which benefits the most popular enemy lead nowadays, EP).
JTR, BB8, RT, Poe, Visas (a counter to the Sith masses that roam around arena these days. Probably won't last when Sith fade away from the Meta).
Than again, I don't have the Resistance leveled enough to try these out, so these are all ideas with no testing behind them.