@Nrm53 Your best bet is Veers, Range, Gideon, Piett and Dark/Starck. I managed to 3* CT3 of the assault battle with this lot where Veers, Range, Gideon and Starck were only r3 and Piett was r5 (what was needed for SEE reqs), but the relic levels can be lower with dark trooper in place of Starck.
Basically the strategy is: survive to get a turn, and hope they target Piett so he counters to get TM on everyone, then just keep riding the TM train through to the end. Gideon is very useful if you can time his mass assist as he can reduce the ewok TM to 0% and if you get a kill then Veers unique leaves all your troopers on 100% TM. It's supposed to be easier with Dark rather than Starck as his damage can get ridiculous, and he can take some punishment in the initial salvos without dying, but Starck also works with his passive TM manipulation thanks to his unique and the occasional stagger.
TLDR - You NEED Veers, Piett, Range (for the assists). Then three from Gideon (almost a lock), Starck and Dark. The more zetas the better, and don't forget the same team can 3* CT3 for the rebel roundup AB too, so they're worth the investment. (When modded correctly they can get 6-10% in P2 or P3 of CPit too).