I'm sorry for your loss. When a friend died recently, two poems I kept reading were Perspective, by Adrienne Rich, and The Lost Garden by Dana Gioia. I read a lot of angry, cathartic poetry too, but these were the two that really comforted me. I hope you manage to find some that are right for your father.

(Perspective)

Our story isn't a file of photographs
faces laughing under green leaves
or snowlit doorways, on the verge of driving
away, our story is not about women
victoriously perched on the one
sunny day of the conference,
nor lovers displaying love:

Our story is of moments
where even slow motion moved too fast
for the shutter of the camera:
words that blew our lives apart, like so,
eyes that cut and caught each other
mime of the operating room
where gas and knives quote each other
moments before the telephone
starts ringing: our story is
how still we stood,
how fast.

(The Lost Garden)

If ever we see those gardens again,
The summer will be gone—at least our summer.
Some other mockingbird will concertize
Among the mulberries, and other vines
Will climb the high brick wall to disappear.

How many footpaths crossed the old estate—
The gracious acreage of a grander age—
So many trees to kiss or argue under,
And greenery enough for any mood.
What pleasure to be sad in such surroundings.

At least in retrospect. For even sorrow
Seems bearable when studied at a distance,
And if we speak of private suffering,
The pain becomes part of a well-turned tale
Describing someone else who shares our name.

Still, thinking of you, I sometimes play a game.
What if we had walked a different path one day,
Would some small incident have nudged us elsewhere
The way a pebble tossed into a brook
Might change the course a hundred miles downstream?

The trick is making memory a blessing,
To learn by loss the cool subtraction of desire,
Of wanting nothing more than what has been,
To know the past forever lost, yet seeing
Behind the wall a garden still in blossom.