I've had to take on a lot more responsibility in my life as of recently, and Im finding it hard to have the time to care for my ageing childhood dog Ace

My family has been helping me take care of ace but 

Ace just seems so sad though, they have joint pains and weight issues and he hardly wants to move, I can't remember the last time they wagged there tail besides when someone offers them a treat 

I just want them to be comfortable and happy in their final years but I don't know what to do for them, and I've had such little time or money to help them, it feels awful having to see ace so sad but I've struggled to find ways to cheer them up in spite of Loving them so dearly.

Does anyone have advice on what I can do or try to cheer them up please. 

Venting / context below  (sorry for the length) 

My family in spite of being the ones who take care of two dogs in the house don't seem to understand animal behavior and don't do much besides basic care and occasionally taking them to the dog park, 

And my family seems to put very little effort into socialy caring for either dog (a dog trainer actually quit on one of my grandparents because they didn't actually understand or apply anything they were being taught by the trainer, and they restored to a shock collar \*that I confiscated\* after, I've been the one having to train there German Shepherd puppy with my very limited knowledge and time since doesn't help that my family effectively sabotages any progress I make) 

So my family isn't going to be much help I think but with me being a full time college student I don't really have much of another option even though I love my dog so dearly and would prefer to spend every day with them. 

Help Caring for my Old dog