Having a guess your friend may have a problem with paramyxo or parathyphoid. (can be similar symptoms depending on strain).
As he had the pigeons tested yet, if not I suggest he gets the droppings tested, throat swabs and blood tests from a renowned vet, look in the BHW you will see a poultry vet in Retford, Notts. I have used them before, very quick and cheap service.
In the meantime, isolate the birds from the others and keep the diet light, with electrolight in the water.