I'd split the stuff into three groups: keep / sell / donate.
I'd start with items to be donated. Arrange for pickup or drop off yourself.
Now we have two groups - keep and sell. If he has any items that he'd like to keep, say to pass on to a family member, this is a good time to say so.
Otherwise everything else gets sold. Market is a bit soft right now, but that wouldn't keep me from liquidating as best I could.
Good luck, and let us know how it plays out.