Oh, my, they're all so beautiful! My heart breaks for you over your recent loss of Jinx and Shad. We lost 6 of our senior dogs over 3 and a half years' time--Cole and Macie crossed to the bridge just a day apart in 2016--so I know the kind of pain you're feeling.
And about your worry about your handsome Fred!
I suspect you've already been giving Fred more gentle attention? Just sitting with him near you? Talking to him? More walks and outside time? Things that will engage his mind and his senses will help him recover faster. Do you think he'd be interested in one of those interactive toys that dispenses treats? I've seen some puzzle toys that looks sort of fun--the dog figures out how to open the door and eats the treats (or kibble) as their reward. Maybe that would catch his interest? It might also help keep his weight up?
Does Fred like other dogs or is he more of a cat person? If he likes dogs, are there any doggy friends in the neighborhood that Fred could visit now and then, or have over to the house for a little social visit?
If it's cats he likes, have you considered adopting another cat to keep him company? At 20 years of age, he probably wouldn't be up to a kitten, but maybe an older cat? Many rescues and shelters will allow meetings between existing family animal companions and prospective adoptees. Maybe you can find a mellow cat that loves dogs that Fred would take a shining to?
It's so difficult to figure out how to help our seniors in this situation. I do hope Fred finds a way through it. Best wishes for both of you