Alrighty, let's see here...
For Henry, I'd recommend swapping out the Carrot-tipped bow for Arcane Nastrond, as it gives Omni +5 rather than atk/def +5, along with damage reduction, and bonuses related to foe's cooldown. If you're using a cav related team, Goad, Hone, Fortify, and Ward Cav skills all work wonders on a horse emblem team. I think you can replace Odd and Even def wave with Def/Res menace (Which you can get from B!Tiki/Leg! Fae/ Zeke, respectively) and give him def/res solo as the S seal, as that will improve his tanking capablities. With those two skills alone, that adds up to a +12 to def and Res assuming conditions are met, which puts Henry's 25 res at a more respectable 37, and kicks up his 49 def to a sky-high 61. Alternative to Foil, you could have him run Ward to counter dragons, or reversal to up defense (you'd need NY Plumeria, or Gatekeeper to get either of these, however), and get the res refine for Nastrond, as that gives him a neat +3 to his res. Oh, I forgot, Atk/Def Ruse can be replaced with maybe Atk/Def snag, or Lull Atk/def if you don't care about the Guard effect.
For Ashe, Give him Iote's Shield Immediately. This removes his innate weakness to arrows. Unfortunately, if you want canto, you'd have to get rid of QR4, to get some sort of far trace (A/S is recommended, but that means saccing off Constense or Elmine, who are much, much better units) If you're feeling like an a**hole, you could run the tried-and-true Close Salvo, Vantage, Time's Pulse 4, and Fury 3 build to have him rupture through everything that gets in his way, but that's more of a general build, if nothing else. Rather than Rein, I'd give him def/res smoke 3 as it ties in well with the dagger 7 effect that his weapon gives (I run a similar build with my Saizo, with Saizo's Start +Eff, Atk smoke 3, and Def/Res smoke)
That's really all I can say, hope this helps!