Honestly, just don't tackle the Champions until you are lvl 210ish and the legendary experience items start being available. The first two bosses are certainly beatable before that, but you will be wasting tickets. Hoard a bunch of legendary and other scrolls. Then, fight the champions with the first group so that you can see the positions. Re roll your team and match hopefully 6-7 or more poses. Then use the scrolls so that your battle team is properly leveled.
Prepare to use dozens of tickets per boss.
I am focusing on the charm bosses right now. I have fewer charm girls, which means that it will take fewer days to get the fighting girls all up to speed. Also, fight lengths and damage are more predictable, since the charm critical does little. I also like to fight both bosses on the same day, so I can use boosters to help the fight go smoother. This gives me down days where I don't fight anybody while I accumulate tickets and experience books.
There is misinformation posted about which gears to use. Using multistat items is not a good idea, since defense is minimal and harmony/critical chance is not determined by your stats. You should your normal single stat leagues/arena gear, but you can also swap in pieces of single stat EGO or single stat defense gear if the numbers work out in such a way that your increased damage from the additional fighter(s) is greater than your lost damage from the bad gear.