My Dad suffered from Alzheimer's, and while he didn't get colds, he had terrible allergies, which had never bothered him before.
When Mom finally decided she could no longer care for him, probably 1/2 a year later than she should have, he only lasted just under 3 weeks in the care facility. He hated it, didn't understand why he was there, and would ask when he got to go home. He didn't know much, but he knew he wasn't home, and when told he had to get better before he could go home, well he apparently knew he wasn't going to get better, and just gave up.
He got pneumonia over Easter, was taken to the hospital and given antibiotics. Then a day or two later my brother and mother took him to see his doctor for a follow up. He seemed to be doing fine and they even stopped at the house on the way back to the facility. Next day, he was observed sitting on his bed picking at his lunch, half hour later, he was gone. Alone with not even a stranger. That was hard to know. It's hard to write about now a few years later.
My father-in-law exhibited similar symptoms, but never got combative. He was diagnosed as having, and he continued to have, a series of micro strokes. Again, my mother-in-law was in denial, waited too long, and nearly did herself in. He never did make it to the local state veteran's home, where he'd at least have been among friends, because he passed on while waiting for an opening.
So sad about your father and father-in-law. My dad had Alzheimer’s too and died of a massive heart attack before things progressed too far. With the passage of time my family has come to be thankful he was taken so quickly and spared years with the disease. He was a retired FBI agent and used to being in command. He knew what was coming his way and to this day I can’t stand to think about what must have gone through his mind when he realized what was happening to him. God was merciful to call him home quickly.