Okay, with his Armor of Darkness spell up, Garin's Touch AC should be 33 and Richard's should be 37 versus an Evil attacker (33 if they're not Evil). If he doesn't have Scintillating Scales up, and I'm assuming he doesn't, Viserys' Touch AC is also 33, though that increases to 49 if SS was cast previously. All of those are very high, plus everyone will have 33 Spell Resistance. That's two layers of defense the Avasculate will have to get through.
And though it is very rarely used, Richard also has 3/Day
Spell Turning he can use if he is targeted. Even if it doesn't turn away the full effects of the spell, it would at the very least reduce the effect by 75% should he be targeted.