The easiest thing here is to count the hit dice and subtract 1 to determine the NPC's rough character level. Though that is far from perfect.
The reason you subtract an HD is that for regular PCs, they get double their first HD to start (it's max value), thus a 2HD monster actually has L1 equivalent HP. (This is not official, just a quick and dirty check to get a starting idea of level).
Acolyte's are L1 using this math. This is supported by the fact that they have 2 HD and are listed as L1 spell casters.
Guards are L1 by this logic as well. This is supported by the fact that they have 2 HD.
Both of these NPCs have +2 proficiency bonuses. The only marked difference from L1 characters is that their stats are significantly lower than a typical L1 PC's would be (which is actually pretty significant). This makes them likely L0 based on starting stats, which is pretty meaningless in terms of setting encounter budgets.
I would go ahead and plan for fights to be harder than if you havehad 5 L1 PCs, as the significantly lower stats of these NPCs is probably going to be a significant barrier to their effectiveness. Perhaps count each NPC as half a L1 PC and see how that works?
Instead, you mightshould probably consider designing one or two (if not all, though that's probably extreme) of these NPCs using PC rules instead and only count those 3 (or using 4 L1 characters for your calculations) when determining your XP budgets. Factoring them based on 5 L1 PCs with this party is going to end in TPKs.
The takeaway here would be that if you care enough about an NPC to be concerned about their equivalent character level, you probably want to go ahead and make them using PC rules. It's a bit more work than pulling a pregenerated NPC out, but it will be worth it.