Gawain help

Euryale + Double David works pretty well provided if you have a friend with a David. Preferably, his second skill is maxed to minimize the cooldown.

I've also tried Euryale + Stheno + David and managed to keep him charmed almost the entire fight with David there just in case he fires off his NP.

Mash + Euryale + Orion/David also worked for me.

The most popular Servants to use against Gawain are Orion (NP drain on NP and Anti-male skills) , Archuria (NP drain on her NP), David (full party Evade), Euryale (Charm and NP drain).

Try this

Frontline: Emiya/ Chloe +David+support Eurayle/Orion
Backline: Mash+ Jeanne+ your Eurayle
Mystic code: plug suit (stun/group attack up/ servant swap)

Try to burn as much of Gawain’s hp focusing on doing damage/ Stalling with Eurayle and using David’s party Evade.

Once the frontline dies stall with Mash/Jeanne/Eurayle using Eurayle as your main Damage dealer.

Use Jeanne’s NP against Exac. Galatine and when that isn’t possible try putting mashes invincible on mash and then combine Mash’s defenses (cd and/or NP if available) and Jeanne True Name Revelation to tank it. Worst case scenario hold onto Eurayle’s NP and hope it charms him and gives Jeanne time to get her NP up.

The basic idea for the backline is to stall for Jeanne’s NP and burn him with Eurayle. Vampirism, charm, Jeanne stun, mystic code stun, whatever, just get jeanne’s NP up.

Need to focus on either defense or charm locking Gwain. I managed with euryale, support Orion as main damage dealers. Eurayle has charm in skill and np and charge reduction skill, Orion has male attack up and charge reduction. Mash provided defense. In backline I think I had David and Tristan for the group evade... And I think steno for more charm support. Two orion np's dealt most of the damage and David was able to mop up the rest. Took a few tries, especially since it is hard to guess whether he will use the charge gain skill and np with one bar left or save charging for the 3rd action.

Maybe try Chloe + Jeanne + support Tamamo with a plugsuit Mozart if you have his arts skill leveled at all.

I used Chloe(Another ending) + Merlin(2030) + support Tamamo(2030) with plugged Mozart(I don't remember his CE) and was able to get it done in a handful of turns. All offensive boosting skills involved were at level 10.

From what you have, You can run a similar setup to mine:
Frontline
Merlin(starting np) + Jeanne d'Arc(Prisma cosmos, +np gain, or 2030-if confident-) + Euryale (special attack vs male, +Arts, Heaven's Feel or Black Grail)

Backline
Mash + Friend Artoria (Archer) + Chloe/David<-(depending on your confidence)

Starting np for everyone else except Mash. Use Volumen Hydrargyrum on David/Mash if you have it.

Get Merlin to NP asap. Point is to keep Euryale alive and np as many times as possible. Use invincibilities (Merlin/Jeanne) first and stall when you can't. Frontline WILL die eventually.

I) Here is when it gets dicey 'cause you can't stall Gawain anymore. II)When Gawain over ATK buffs, single target Mash (+invincibility if not close to winning) and defense up for Ex Galatine.
III)Use Artoria's heal if necessary, keeping her alive is worth more than 10% gauge.

*Note: David's evade can save party or have Chloe help Artoria clean up.

Mash + double Euryale worked for me. Backline: any support with def/attck buffs, Chloe/Tristan/David. Mystic Code: either Atlas or Chaldea combat suit.

Tbh I don't know how my alt acct could've gone past him if I didn't have enough mats to max Euryale and lvl her 3rd skill to lvl 8 immediately. Having Orion wasn't enough for me bcoz u need to keep him from using his NP until ur def buffs was up. The charm was inconsistent though so u need to time Euryale's NP as well when he is about to Excaliblast your party.