miguel: this poor boy omg if you caught him jerking off he'd probably never touch himself again. his cheeks would be red as fuck, and he'd be stumbling to pull his shorts back up, begging you to act like you didn't just catch him going that.
eli: this mf would make eye contact and keep going, letting faint whispers of your name fall past his lips. he's secretly embarrassed but refuses to let it show since now is the perfect time to let you know how bad he wants you.
demetri: the absolute shock of seeing you would probably make him cum even if he wasn't close. he'd squeeze his eyes closed tightly and pray to god he's imagining you, trying to bargain with the universe to make you disappear.
robby: he wouldn't be too embarrassed but he'd stop out of shock and quickly pull his shorts back up, apologizing for not locking the door. when he sees you don't mind, he's probably start to tease you by touching himself slowly or moaning your name.