How can I best deal with my father-in-law's dementia and anger?
Re medicines-ask doctor if med can be given chopped up and mixed with a food patient likes. Consider a certified aide in home for a few hours or an adult day care center for some respite. Cheaper than assisted living. Keep child with patient when another person is present. Don't argue with patient. Consider playing along with fantasies or nonsense as much as possible. Find what makes patient calm.
This might sound odd but see if you can find music he likes. We got a Roku box for our television and a Netflix account, and have found all kinds of old Dean Martin, Frank Sinatra, Bobby Darin and Tom Jones variety shows that we can play for her non-stop, and the service also includes Pandora radio where you can put in an artist he likes and it will continuously play music from that genre.
We stumbled upon this recently during bad bad sundowning episodes where my mother was absolutely beside herself that she had to go home because her parents (who'd be oh, 118 and 122 at this point!) would be worried sick about her. None of the usual distractions worked, in desperation we put on music. It worked like a charm, especially to familiar songs where she knew the melody and lyrics. In an instant she went from really combative and agitated to singing along and talking about the song.
We also have a dry-erase board on the refrigerator where we have a checklist of my mother's "vitamins" that we check off as she gets them. She will get agitated that "she just took them" or "took 19 of them after breakfast" so now we can just go to the refrigerator and "check." We've even gone one step beyond and had her do the honor of making the check-mark on the board, to help her feel part of it and to help calm her that everything was a-okay. Experiment, think stubborn 3-year old.
Good luck, it's hard, stay upbeat and creative no matter what!