He isn't capable of the revenge/spite actions you're assigning to him (I am a dog behaviour consultant, I am not pulling this out of my arse).
He may be showing signs of doggy dementia, or he may have been conditioned to go in the house, like thats the correct spot, or he may feel worried/insecure outside (many elderly dogs do) and so feel its not safe to toilet out there.
Eating grass that then makes him sick suggests some sort of tummy/digestive issue, yes he is eating it to help him bring something up, but that is to make him feel more comfortable, how could he possibly understand that cleaning carpet is a pain in the backside for you or that living with the smell of puke on things is gross?
Biting when handled - its sore its uncomfortable its scary, sometimes more so than others, if you've ever ignored him growling or told him off for objecting, he may well think there is no point communicating more subtly and just drop those behaviours and go straight for the bite.
Dragging behind/pulling on walks often linked to pain, and potentially feeling insecure/anxious so wants to stop or wants to just charge through it and get it over with - both/either will reduce anyones ability to listen, think, learn, exercise impulse control.
I do understand how emotionally draining it is (and physically at times) living with a very old dog - our Tibetan Terrier died at 17 years old, a few days after christmas. For several years he'd had to be carried up and down stairs (he would attempt do them himself but it wasn't sensible to let him) and would occasionally wee in his sleep or not get himself to the door in time. He had several vestibular attacks, needed a fair bit of medication and support, couldn't be left alone as he was blind and would get himself stuck somewhere in his search for his favourite toy.
We understood though that none of his behaviour was revenge/spite related, thats not something dogs are capable of - he was just trying to keep himself comfy, do what he wanted to do (because dogs are self-centered little beings, they aren't capable of human levels of empathy!), keep himself safe etc.
We found that Vitofyllin really helped cut down on the doggy dementia moments where he'd grind to a halt and forget what it was he was trying to do. We also gave him Lions Mane which also seemed to help.
To keep him outside long enough to go to the toilet and ensure he felt generally relaxed and happy out there, we'd scatter some stinky fish kibble (use whatever your dog can eat) for him to sniff out which being blind, took him a while. The sniffing around and gentle movement both relaxes and increases the chances of going to the toilet though he did need total supervision as when his feet found the ramp up the steps that would trigger his 'going back inside' routine even if he hadn't been yet.