This is a tricky question and ultimately one that only you can answer as you know your pets the best!!
We can only advise you based on our own experience and feedback from our clients. Basically dogs usually like to sleep alone in shallow nests, near to the other members of the pack, but prefer to have a space of their own.
In the domestic environment we usually deny them the chance to make a nest, providing them with relatively unyielding bedding such as pads or blankets. As a consequence dogs will often replace the warmth and support they should get from their bedding by snuggling up to each other. As a result owners often conclude that our dogs like to sleep together.
Unfortunately it often turns out that the dominant dog, often a bitch and often the smaller dog, is simply using it’s mates as convenient bedding. Once they get a comfy pet bed the dominant pet will then take the bed for itself and push everyone else onto the floor.
At its worst if you have bought a large bed for two dogs, one large and one small, you will often find the small dog in the middle of a huge bed and the large dog on the floor. You end up with an unhappy pet and you’ve wasted your money!
Only you know your dogs so only you can decide which scenario yours fit into!
The only exception to the above are Cavalier and King Charles Spaniels which, because they were specifically bred to sleep in piles , will almost always share. (They were bred this way because King Charles II liked the aesthetic of piles of dogs around the palace)
If you feel certain that your pets will sleep together, or have Cavalier or King Charles Spaniels, then it is fine to get one bed for multiple dogs. Just combine their weights and get the bed for the total weight of the dogs. Refer to the Size range page.