u can use invisiblity and see_invisible given its a pretty small project

also, if u have invisiblity verbs, and u dont want them to see u, even though ur using invisibility, u can use for urself invisiblity=2

u can only see things that have invisiblity = or less than your see invisible variable

therefor if the say item A is invisible = 1

and theyre see_invisible = 1
they would see things of invisiblity = 1 and invisiblity = 0

invisiblity = 0 is used by everything at default

for invisible = 2

if ur see_invisible = 2

you see things of invisible = 2 invisible = 1 invisible = 0

so you would still see the stuff of invisible = 1, but if you want to make it so you cant see it, but you still wanna be invisible to others, there are more methods.

such as instead of invisible, to put icon = null
that would make ur icon nothing, so u wouldnt be visible.

theres another way you could also do, 3 invisibles so that something else appears over the object if ur not supposed to see it.

Look up invisibility and see_invisible in the DM Reference. Also look up images as they're related to the subject.
Stuart brought up a pretty suitable possible solution here; though the effect is visual only so players will still be able to bump to the NPC's they don't see, though you could account for things like that if you really wanted.