Just a few more thoughts on what has been posted above...
I know that most websites seem to suggest it be done in three days, but could it be done in two days by a few relatively fit people? The distance seems manageable, although I do note the massive elevation changes...
Very feasible to do in two days. A few months ago I took a few people out, and even with disaster, we still made it. (Disaster = 38C day, and the soles of one of my colleague's shoes completely fell off 1/2 way up Mt Solitary, and the colleague also didn't get my note about bringing extra water).
Does camping at Kedumba River seem feasible?
Very feasible. There are two campsites: the proper one a bit further south, but I think it is closed, and then the place where the trail intersects Kedumba River. We stayed where the trail intersects the river.
Here are my notes/pictures on AllTrails:
https://www.alltrails.com/explore/recording/big-08f0efeIgnore the pace - again, equipment malfunction. If you start at 8am you shouldn't have any dramas making Kedumba by sunset. At the river it doesn't look like there will be any good camping areas, but up to the right is a place that can easily take 3x tents - flat and quite sheltered.
What is water like on the way?
We planned for no water from Katoomba to Kedumba River. There turned out to be a few very small streams along the way, and apparently there is a water tower right around the fork up to Ruined Castle. However, I think the tower is on the main track, and we missed it.
One of my mates camped up at the top of Mt Solitary end of March and there was water available. Here were the coordinates: -33.78357, 150.33008
However, I wouldn't plan on water being available, and it probably needs to be filtered (same as at Kedumba River). Just for reference I encouraged everyone to bring 5 litres for the Katoomba -> Kedumba stretch, which was just barely enough, but then again it was 38C and we walked excruciatingly slowly. Walking back up from Kedumba River to Katoomba there are several places to fill up, so I don't think we ever carried more than 2L at any one go.
https://www.gaiagps.com/public/2ijpd5T6XaeBO7GPApQ4g6bX/Ignore the red markers.