It looks to me like the groom (or someone) HAS booked a hotel room.
This is definitely NOT his own bedroom. Look at the light fixture…look at the pillows and the bedspread…look at the entrance and how they walk past the bathroom. All typically from a hotel room.
Probably the reason why the FIL is sprawled out on the bed is that there was no other place to sit to take the photo with so many people in it, knowing how small hotel rooms can be.