I can 4 turn it but it's not completely reliable because I don't have Kaleidoscope. Euryale/Emiya(NP2)/Waver/Arash
First turn try to get some NP with Emiya and Euryale.
Second turn use Projection and Waver's ATK and Def up, then UBW.
Third turn switch Euryale with Arash, use his NP charge skill and Waver's crit up, the Mystic code ATK up and then Stella.
Fourth just use Euryale's Arts up and explode Gawain.
The only issue is that if either Euryale or Emiya aren't able to charge enough NP on the first wave then it takes 5 turns. Also the second wave may not die from Stella but you can finish it off with the other two cards.