I think they’re okay to exist, but it might be another story if both sides are separately usable. Though, by that logic, you also won’t be able to allow two single beds placed directly next to each other. I’m not really sure what the answer is in this case as I don’t believe there’s any specific rules regarding this.
I think it would be safer to go with single beds. But in my personal opinion, players could act inappropriately regardless of if the bed is single or double, therefore I don’t think it should matter (again, this is an opinion and not based on whatever is deemed appropriate by Roblox).