Both tracks are weather dependent - in the dry neither of them are going to be a problem, in the wet....I'd make other plans.

The steep bits of Deddicks are right next McKillops bridge, so you can go and do a recce before committing to take the trailers in there - my wife's Pajero made it up the climb with a 1700kg camper on the back without any issue on all terrain tyres. There is an alternate all weather road along the river if you don't want to tackle the climb onto high ground.

Davies Plain track is a similar story - once you cross the river at Tom Groggin there are a couple of short climbs, but once on the high ground it's an easy trail - again no issues with trailers in the dry, but could get nasty in the wet. The bad weather option would be Khancoban->Thredbo->Snow River Way->McKillops

My suggestion would be to do Charlotte's Pass and Kosciuszko as a day trip returning to Khancoban on Day 3, Day 4 would become Khancoban to DPT, Day 5 DPT to McKillops, Day 6 McKillops to Orbust, Day 7 Orbust to Blue Water Holes. This would be pretty conservative, we did Tom Groggin all the way through Deddicks with a trailer in a single day (then drove back to Sydney that night :-))