The number of dogs permitted per dog-friendly hot tub holiday cottage really depends on its size and location. A small property usually accepts only one pet but if booking a large country house that is surrounded by acres of garden, the number could go up to several dogs.
The number of dogs permitted at each hot tub holiday accommodation should be clearly stated. People sometimes try to bend the rules by asking if two of their small breed dogs would be equivalent to one big one. Because we do not get involved in any booking process, you would need to ask the property owner personally.
Please note that dogs are never permitted inside a hot tub. The chemicals used to sanitise the spa would not be good for them.