My guess would be kidney disease or cancer for Nellie. Like someone else said above, I would imagine its not a test taking two weeks to come back but rather monitoring again in two weeks (to see if kidney values have risen or if a tumor has changed/spread). I do feel bad for the poor thing. He was from a terrible breeder, is totally inbred and unhealthy from day 1, and hasn't exactly been treated well by his current owner so it was sort of inevitable that he would die young, poor thing.
Also in regards to her lesions, 100% I think its actually related to her stomach. I don't think she has endo. I lowkey think her stomach surgery has created lesions that has attached to her muscle. But thats just me.