Use Magic Device (page 109, Core Rule Book) says
Use a Scroll: Normally, to cast a spell from a scroll, you must have the scroll’s spell on your class spell list. Use Magic Device allows you to use a scroll as if you had a particular spell on your class spell list. The DC is equal to 20 + the caster level of the spell you are trying to cast from the scroll. In addition, casting a spell from a scroll requires a minimum score (10 + spell level) in the appropriate ability. If you don’t have a sufficient score in that ability, you must emulate the ability score with a separate Use Magic Device check.
So, my 3rd level rogue has a 10 INT, 8 WIS, 14 CHA, a +12 UMD, Eldritch Conduit and just got a Scroll of Magic Vestments.
He also has a Scroll of Shield he'd been saving.
Eldritch Conduit (page 7, Magic Tactics Toolbox) says
Eldritch Conduit (Su): Survival in the Mana Wastes between the nations of Nex and Geb can depend heavily on locating sufficient magical equipment, which sometimes involves stealing power from a wand or scroll to power a more necessary one. As a full-round action, a rogue with this talent can use two potions, two wands, or two scrolls. Each item is expended or loses a charge as if used normally. The rogue chooses to gain the magical effect of one, but calculates its effects using the caster level of the other. The rogue must still succeed at a Use Magic Device check to operate scrolls or wands unless some other ability allows him to do so, but makes only one skill check to operate both items.
My question is Would I need to emulate an 11 INT, 11 WIS, 13 WIS, both an 11 INT and 13 WIS, or none since you only make one check for both? I'm assuming the CL DC would be 21 based off the Shield spell?