In the US, it's quite common that hotels allow up to 4 people in a room, though some may limit it to two adults.
Do hotels allow 4 adults in one room?
Hotels don't usually allow 4 people staying in a single room.
Are hotels strict about guests?
Can I bring hookup to hotel?
Most hotels are relaxed about this sort of thing. If you're worried about it, Booking.com have a 'special requests' box when booking – I'd suggest using that to let them know someone else is joining you.
Can someone sleep over in my hotel room?
If the other person just sleeps on the floor or together with you in your (single) bed, you can just have them “sneak in”, most likely no-one will notice or care as long as you don't cause any noise or other complaint. No, unfortunately it is not possible for someone to sleep over in your hotel room without paying.
Why are visitors not allowed in hotel rooms?
It differs from hotel to hotel; some hotels are not allowing any visitors in the guests rooms due to security reasons. Some hotels allow visitors on arriving at the property but every visitor has to register with the Front Desk.