Doug, grieving is a difficult process and all you can do is be there for him. Grief comes like ocean waves on the sand, in and out. He will start with more grief, fewer moments of peace, then over time it will shift to more peace, fewer moments of grief. But it's a long process, can take several years. It's hard to talk about because it's thought by some to be "unmanly" and one needs to "keep a stiff upper lip." But grieving is normal. And one of the things I learned in graduate school is that sometimes a spouse will follow their loved one within a year. Particularly if they were deeply "entangled" (a term from quantum physics) - I just want you to be aware, and not feel upset if that happens.
The biggest help (assuming pathogens are under control) will be providing him with nourishment that supports and sustains him, physically and emotionally. I don't remember his living situation - is he in assisted living or is he living on his own? If he's on his own, and if she was the major cook in the family, he may need some help getting fed. I like David's Umawangowango juice (I know, that's not the name of it, but that's how it looks in my head - I'll have to go look it up and edit this to get the right name)
. UMLINGO WAMANGCOLOSI / MAGIC OF NGCOLOSI
Hugz to you and your dad, and all your family.