I know what it is like to lose a family member with four legs.
When our last, and final, family dog (Jess) had a lump that was "iffy", we decided that at the age of 14 an operation was probably too much for her (A border collie). It was about 8 months later that it kicked in and affected her brain, and Mum and I took Jess to the vet, both of us crying. He (the vet) came to the house later that day, and our dear girl went quietly.
What you are describing sounds like the other dog, that Mum & Dad inherited when my cousin died, aged 30.
Todd was a Norfolk terrier crossed with another that I can't remember (we used to call him The Ginger Whinger, as he begged for food, something terrible), and he lived to 17 yrs old.
He spent his last months sleeping, getting out of bed and piddling on the carpet, but come 6pm, he was stood at the door, waiting to go to the pub!
I just wanna give you and your family a great big hug, coz I know exactly what you are going through.
xxxxxx Jane xxxxx
Some are born great, some achieve greatness and some have greatness thrust upon them.
The rest of us are a bit crap.