Cats are not party animals and don't really like exuberant social gatherings. It's a good idea to sequester your felines in a quiet part of the house before company comes over. Equip the room with their food, water, litter box and their favorite beds or blankets about two hours before guests are due to arrive.
If the room is carpeted, place a large garbage bag underneath the box to capture any litter and to guard against any mishaps. Put a notice on the outside of the door that says “Do not disturb.”
If your cats are particularly fearful, it may be a good idea to spray the room with a feline pheromone spray or plug one into a wall socket several days in advance. These sprays and plug-ins emit synthetic versions of naturally occurring feline facial pheromones, which cats deposit when they rub their cheeks against surfaces, marking the areas as safe and familiar. Thus they can help to make a cat feel less anxious in what could otherwise be a stressful situation.
There are also special calming collars made from all-natural products that can be placed on the cat along with her normal collar. The effects last up to a month.