Responses
Option 5: they hide in a closet and continue to have sex.
Problem: it smells of sex and senpais are suspicious.
Option 6
The people leave and they get dressed and run out before they come back
Spoiler....
Your option 4 is nearly right. They didn't open the door and go back...but the chubby guy got suspicious about Alex but didn't know with whom he sex...
4 for me ヾ(❀╹◡╹)ﾉ
Prediction time!
*Knock knock knock!*
Option 1: They clean up in a hurry and open the door all casual like. Problem: Messy hair and flushed faces, boners probably still hanging around, overall atmosphere will spell Sex was happin'!!
Option 2: One of them hides in the room while the other opens the door, like I was just having some quiet me time XD Problem: The senpais saw them go off together to have lunch so to be alone is super suspicious hmmm
Option 3: Invite em in for a 4some XD Problem: yeah right!
Option 4: Just ignore the knocking, only Alex and the TA have the key, the senpais fuck off since the door remains locked. Problem: the mood will be ruined, the slightly chubby senpai will be even moooore suspicious because i bet he knows Alex has a key to the room.
Let's vote ya'll
Option 4 I reckon. (=・ω・=)