sorry your dog isn't doing well. I have yet to put one of my dogs to sleep but i just put my cat that i've had since i was in the 4th grade to sleep. She was 17 yrs old and had i believe stomach cancer. I did a bunch of tests to try and figure it out but but couldn't find anything. After we had to put her to sleep my dog Penny had a litter of pups which helped make me feel better. The pups didn't replace her but made me feel like things came full circle. Everday those little guys put a huge smile on my face.
I hope your family is doing well