Can I beat the challenge quest with my servants?

From what I can see, you have some decent levelled servants so shouldn't have much trouble. Some people actually done it with pure 3 stars which is amazing in my perspective.
https://youtu.be/wQ9T5bu2md0

I had similar servants as you, and I borrow a Jeanne (Lv90 7/7/7 with Prisma Cosmos) and use Chloe and Emiya with Mash, Herc and MHXA backing up. But really the MVP in this setup was Mash, Jeanne and Chole, so I guess if I start off with this line up, I might not even need to use 3CS. I use Chalea Mystic code to give me heal and evade in this quest.

Maybe give a crack first, it only cost 5AP and good luck!

Use mashu with max skill and support merlin. Best archer for this challenge is david because he have evade, buster np(merlin 3rd skill) and 3 art for art chain. Use mashu taunt & invicible in first turn to gain np. Try to get art chain every turn so you can spam mash & merlin np. Best ce in this quest is black grail for david & prisma cosmos for mash

You definitely can. People use Jalter + Merlin combo and they did it, or you can do it as I tried, and it works, just a bit painful and might need CS if you messed up: Chloe + Mash + Support Jeanne, back line Euryale + David. Mystic Code: Chaldea Combat Uniform.
Get Jeanne's NP ready before Salter's NP for Invincibility. Tank the rest of damage with Mash's defense up skill or her NP. If you fail to get Jeanne's NP on time, swap Mash with David and use evade. If the skill is on cool down and Jeanne can't NP, stun with Gandr or Jeanne's skill. If nothing can protect you even Jeanne's NP damage down, that's why Euryale and Mash are on your back line.

Then just do it over and over again. Chloe damages, Jeanne protects from NP, David for backup. Prioritise Chloe and Jeanne for NP and protection. Creep your way slowly to 3mil HP. In 94 turns.
It's really painful, but it works. David doesn't have to be max leveled, as long as he has his 2nd skill. Mine is still at lv40 4/4/-.

Or just Herc your way out. You can put him in the combination above as last standing too.

I beat it with this setup and a merlin support who was 7/7/7. 3 command seals used to revive once after the last break.
If you can manage a similar setup, you can win it.

Kuro + Mash + Support Merlin is enough to clear the quest.

Tamamo Caster + Vlad zerker+support Merlin, backline Mash + CasterGil + Herc. Use 3CS when Salter left 800k+ HP at final HP bar.

Easily.

It's more than enough to beat Salter challenge quest. You actually don't need any Waver or Tamamo or Merlin for the challenge quest.

Just play safe and for the team comps, the ones mentioned by Pandarilla is powerful enough to carry your way to victory.
If Tamamo or Merlin or Waver died there by taking random Crit from Salter then you're gonna depend on Command Spell, too risky. Unless you've double Waver or Merlin on your party then it's up to you.

Pretty much, i can guess how that teamcomp works. If you want to see the explanation below then you're welcomed.

Mash can mitigate Salter damage to your party a lot by using her skill and NP, Jeanne for party wide Invincibility + Def Up + regen + NP damage down.
Chloe NP can reduce Salter chance to crit, her NP is spammable which can also mean Salter will just depend on her atk up to hurt your entire party. Don't forget about Emiya atk down and triple Art cards in his deck to ensure you can use your party Art chains as much as you can until you can clear the Challenge.
Combined with Art team stiff, solid, tough and spam playstyle, Victory is already guaranteed for you.

Btw i also don't need any Waver or Merlin or Tamamo there, i use David + Tristan + friends David. Rotary party Evade + decent Heals + skill seal + def up/survivability CEs, it's also a guaranteed Victory for me. I use Atlas Academy for maximum survivability, sometimes Salter stackable def down debuff is really nasty.

Vs Salter in a nutshell, rinse and repeat tactics :
Salter use NP - David use party Evade - Salter use NP - Tristan use party Evade - Salter use NP - friends David use party Evade, both David have their own Def Up and heals and that's nice. Tristan and both David will keep using party Evade until Salter is dead.
Atlas Academy MC for emergency situations, if Salter raise her NP bars or someone in my party have very low HP or etc.

No Command Spell used.