Stealth is only needed if you’re doing anything more than sitting and watching, like trying to hop buildings or set up something big. If you’re just waiting for the others or doing minor things like drawing your weapons I won’t make you roll for it.
Situational camo you know. If you're standing still and colored the same pattern as the brick, sure, adv on a stealth check. But it's not an active camo that'll change as you move, at least not unless you're moving very slowly. The classic method I use Minor Illusion is to Solid Snake myself some foliage or rubble "around" my character as he slowly crawls forward.
You'll get half-cover if the ally is in any position to defend themselves. That's effectively a +2 to your AC i believe. Only way you'll get 3/4 is if the ally is even bigger, like large sized aka a horse or some such. And of course there could be other risks involved with such a thing too, like your ally getting hit if the monster rolls a nat 20 or something.