There one thing to keep in mind while making games:
you make games for fun, so don’t be afraid of “poetic license” game should be fun first then accurate if possible and if accuracy/realism is adding to gameplay.
In cases of your game all you need to do is pretend about having multiple character.
From code pov all you need is single pawn, and just pretend it is team of 4 adventurers.
All that pretending may be done in hud.
So having 4 imaginary adventurers does not mean you need to code 4 pawns for player.
Game code does not need to be structured exactly like world/gameplay is.
ps.
There is nice game just like you want on steam: Legends of Grimrock