Hi,
First, I am so sorry to hear about your father's stroke. It sounds like you're doing all you can to continue to keep him active, up to and including taking up and helping him with his hobby.
Jumping in on painting can be overwhelming, especially if you don't have anyone to mentor you. Here, you will find mentors willing to help you. Sounds like your dad is a man who likes cars, so I would recommend to look at the some of the car threads on here (Mark Jones who posts as Scale Master is an incredible builder and painter who has written for magazines including FineScale Modeler; I've worked with him and he knows his business). Here's a link to a recent thread of his builds for 2021:
https://cs.finescale.com/fsm/general_discussion/f/9/t/189927.aspx
Also, peruse the paint threads and don't hesitate to ask questions, especially about gloss coats. They are tricky affairs, especially on cars. Here are some links to the site about smooth paint finishes and clear coats (a little dated but still valuable):
https://finescale.com/online-extras/how-to/2021/05/the-best-spray-paint-clearcoats-for-scale-models
https://finescale.com/online-extras/how-to/2021/05/make-rubbing-compounds-work-for-you
https://finescale.com/online-extras/how-to/2021/05/5-steps-to-get-the-smoothest-paint-finish-possible
https://finescale.com/online-extras/how-to/2021/05/polishing-pads-get-the-rough-out
Lastly, you seem overwhelmed. Don't despair! As with anything, modeling takes a while to learn, and enjoying the process is a big part of successful scale modeling. The setbacks you've experienced are you learning the ropes. Don't be hard on yourself or beat yourself up. You'll get there. Here's hoping to see more from you, and all the best to you and your dad.