Can you hire a cleaner to get the basics done every week so you can concentrate on the big picture stuff?
One method I have heard of, but not tried myself, is to:
Pick a room and forget about the rest of the house.
Pull everything out of every cupboard in that room
Put back in cupboards only the stuff you want to keep, everything else gets put in a different room / location to be dealt with later.
Keep on going until you finish that room.
Close off room.
Deal with everything you took out of the first room ie donate or throw.
Repeat with another room
Keep on going until you finish the house. It may take days to do each room and months to finish the house, but you will get there.
When you get to rooms such as the kitchen / bathroom / lounge room, just go cupboard by cupboard.