That's so heartbreaking. 
You'll get a lot of people offering all sort of tips, I'm not usually one to do that. 
Yet, this is one piece of information I cannot pass up on letting you know about. 
It's solid research and in this quick YouTube interview it explains it very simply (and in only a few minutes). 
Please do make time to view: 
https://youtu.be/9405FgR2Kik?si=t7ZmItmIJpr2uQzC&t=494 
(I've set it up to start at the right start time for you).
It’s vital for you and our dad to know.

P.S. 
If you do have a little more time, this might be worth viewing also, just for your own information https://youtu.be/pZeDbELYb0M?si=VZdJVWMzuNgNOLRu