help with last exhibition quest

I believe your team lacks a good damage dealer. Out of those I would suggest putting the CE on either Cu (because he can stay on the field the longest and therefore make good use of the damage plus), or on Chloe (in order to get rid of Nero in the end)

Imo definitely bring Tamamo for skill cooldown reduction, heal and NP charge. Jeanne as a ruler is also good for stalling and healing your team. If you have a leveled Mash I'd bring her as well to absorb some of the enemies' NPs.

The debuffs and poison starting from the first round will be really rough, so you should decide whether you want to get a support to get rid of those, or find a good damage dealing beserker (like Cu Alter).

All in all I'd suggest

Cu with MLB CE
Tamamo
Medea Lily or Martha support (to remove the debuffs and poison)
Jeanne
Mash (if you have her leveled)
Chloe

Or

Jeanne
Tamamo
Cu Alter Support with MLB White Rose CE
Mash
Cu
Chloe with MLB White Rose CE