Display your strategy. You can just do one, or you could do multiple. I'm referring to the following missions:
Beach Brawl
Royal Royale
Hidden Truths (1 & 2)
Heirs of Fates (all of them)
I'll start.
For Hidden Truths 1, pair up one of the other two with Owain, preferably Severa. I say Severa because she has the Armorslayer, which you can pass to Owain without wasting a turn. Owain is going to be MVP here, picking off everyone with the Levin Sword. Try and give him all of your star boosters, except the Speedwing which you should give to Severa. The point is to have Owain kill everyone you can, if you cannot, pick them off with Inigo. Shouldn't be that hard. I have Severa paired up because even though they give the same pair up boosts, Severa does more damage so in the worst case scenario Owain and Inigo die, you have Silver Sword Severa sitting all cozy in the back.