Level 5A Dark Side

Kill Lobot first, then Chewie second. Save the other mobs for last.

You should be crushing that mission based on your characters. Sorry, I don't know what to tell you other than maybe your gear is to low. What gear level are you? If your team is below gear V you might want to boost it to VI

All level VI Gear. Chewie is gone crazy. Sometimes 3 attacks in one turn. He gains turn meter faster than Dooku and regains health in 3 turns.

Yeah that Chewie seems a bit glitchy but the level after that is more annoying. You will fight against only Luke Skywalker (with lightsaber) but he will do an amazing damage. I guess these two levels need some rework.
As for getting past those levels i suggest you to try them when you get at least 2-3 toons to 5-6 stars and gear level VI-VII. Otherwise you will use so much energy on those as i did :|

I got a team of Phasma, Sidious, Daka, Talia and the geonosian Soldier all of them about level 53 when I did those levels and I had no problem at all. My gear is eigther VI or VII. I don't know why these levels should be hard. I found the both last levels of Dark side 5 much more difficult, because you face multiple Jawas!

I was ready And scared before this level and it turned out to be easy with
Sid 5
Dooku 4
Vader 4
Phasma 3
Daka 4
All gear 6/7 except Phasma who had 5 I believe. Just make him Buff Immune with sid