I don't use IG-88 in the arena. He gets targeted early and doesn't have enough health to survive. He dies before getting to take a turn. Lando is starting to fall away because he can get stunned, slowed, or ability blocked and can die before getting a 2x AoE attack done. A very fast Boba Fett getting in his ability block AoE can really help. He can also ignore taunts, or debuff a taunt.
Having two taunters won't always help if your opponent removes your taunt, or if they have a powerful AoE. Sun Fac will clear the STH or RG taunt and then everyone will go after your attackers, who won't have the health to survive for long.
I'd also recommend Sun Fac, since he can remove buffs, sometimes automatically on a counter. You will want to clear taunts and all those Rebels with a green 2x floating over their heads.