Question: "My client wants me to take photographs which conflict with the laws of physics. What should I do?"
Answer: The laws of physics _always_ win. Sorry.
The camera needs a certain amount of light to capture the exposure. Assuming the goal is to not have blurry photographs (if blurry photos are ok, you're in luck), then if the camera is not moving and also if the subject is not moving, then almost any amount of light is "enough" light because you can put the camera on a tripod and leave the shutter open as long as you need (trust me on this... astro-imagers take photos that involve HOURS of collecting light all to make a single exposure (although there's a LOT of technique that goes into this... it's not just a single shot to produce a single image.)) You won't need hours for rooms lit by holiday lighting.
The point is, there is a reason why they invented the tripod. Sometimes the tripod is the right tool for the job.
If the hotel won't permit the use of a tripod, and the amount of available light is inadequate for hand-held photography given the equipment you own, and you can't bring in your own supplemental lighting (or at least don't think you'd be satisfied with the results of any supplemental lighting you could manage to bring) then you're sort of at an impasse... pick a different venue or find a way to change the shooting circumstances.
If you're shooting hand-held, then you'll need a flash and you'll "drag the shutter" -- meaning you'll set a longer shutter exposure time then you'd normally consider. This is because the flash on your subject will be very brief but as the shutter continues to remain open the ambient light will fill in the background of the room.
As I dig through my own photos of holiday lighting (using no other lights) I see I have settings like ISO 3200 or 4000, an f/2.8 aperture, and shutter speeds around 1/40th to 1/60th. I have other shots that don't have people in them... just the room... they were taken at much lower ISO but the shutter speeds are also much longer (too long for a person to be able to remain still to avoid any blur.)