The suspicious patch needs to be checked by a vet, I would try to get an appointment on monday, as wednesday is nearly a week and its best to get fungal under control quickly (If thats what it is). If your vet shines a special light over the piggies and delares them fungal free because it didnt florress, Dont buy it. Not all fungal piggies can get floresses, that does not mean their problem isnt fungal. (However we dont know its fungal, So go with what the vet advises, just warning you that some vets arnt aware of the not floressing)
Please claim back any vet fees (or try to) from the rescue. Also, take a picture of the patch today (even though you cant show it to us), as proof that it was there when you got the piggies home (ie she rehomed them in that condition) as that will back up the complaint youve already made.
As for the weights, They are very low. Try not to give them too much veg to start with as it may upset their little tums to have new things. Also, the less veg they have the more (fattening) pellets they will eat, so dont go crazy with the veggies.
Atleast, thats what Ive picked up from other similar cases. Anyone correct me if they think I'm wrong pleasee!