I'm so sorry for the loss of your Dad, OP.
I get it. For the first year after losing my lovely mum, who was such and active, involved grandparent, my in-laws moaning and general un-involved-ness really made me angry.
That we all lost the fab, loving, engaged grandma and yet two miserable grumps who can find a reason to complain no matter how tiny were still here, making the world a more depressing place felt so completely unfair.
As I got more to terms with bereavement I didn't compare what we'd lost to what we still had so much.
In-laws has always sucked the happiness out of everything; it's why our visits (also 2 hour drives) were very short. They'd find fault in a perfect sunny day.
They haven't changed and it was unfair of me to resent them being themselves.
But it was part of grieving, and perfectly normal. A kind of "Why are they having years of life to just moan when Mum could have had those years and really LIVED them?" cry to the universe.
Must compassion to you, OP. Again, I'm sorry for your loss.