Sorry that you and your family are going through this. There is nothing worse than knowing you will be losing a pillar of your existence.
I have been through this and the only advice i can offer is to spend as much time as you can with him. Make sure you are there for your mom as well as your dad, as it's going to be hardest on her.
Also, don't forget about yourself. You too are suffering along with all your family and friends, and you to need to grieve. Your wife will want to help...let her.
It sounds cliche, but try and dwell on all the good times/things and focus on them exclusively.
Godspeed to you and all those affected.
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