This. And to add it is unlikely that a PM is going to be inconclusive, as a few people have pointed out there will be signs in the organs. Sadly more rabbits could still die and so yours are still at risk whilst you aren't certain what you're fighting.
This, and can I just reiterate that a PM will NOT be inconclusive. All causes of death result in certain changes within the organs, so this combined with the other information you pass on to your vet, will mean he will have a very good indication of whether it is VHD. I suspect the vermin are probably carrying this, and it may well be that it is your single buns that have died SO FAR, because the mice have felt safer going in where there is just one bun instead of 2. The buns themselves don't need to come into contact with each other not when it is airborne disease, and you have vermin on site.
You really do need to know what you are dealing with, as you could inadvertently pass it on to someone else's bun, resulting in another death, even through stroking a dog or something and then that dog going home to where there are also rabbits kept, and the dog then sniffing the rabbits, could still pass it on, resulting in more deaths if the rabbits are not vaccinated.
Oh dear, Jack's Jane says that this disease doesn't have to be reported now, but hearing about it when so close to myself, even though my buns are vaccinated, still makes me uneasy, and I worry about if vets don't know about it, and aren't able to let people know that it is in the area, if it might result in an epidemic or something.
To be perfectly honest, there are way too many unvaccinated rabbits about for whatever reason, with owners simply not providing the care that they should be. As far as I'm concerned, ignorance is no valid excuse, because even if you have never had a rabbit before, or any pet for that matter, you have a responsibility and duty of care towards your pet, to make sure that you do know what you need to before taking them on, especially when it will determine if they live or die.