I got through tier II with Wedge (L), Biggs, Lando, Scarif Rebel Pathfinder, and R2. They're my arena team so I knew that they would be able to handle the PvE characters, especially since I had used a weaker version of Wedge and Lando on the first tier the last time the event was around. I eventually just hit auto with the first tier and cleared easily. I auto'd the tier II as well but that one I lost more protection, but the heal from Wedge was essential for SRP. All I can say is keep trying.