RD you have to give both yourself and them a break! It will take a while and some success and not to get things in place. I think mucking in with them and making it as fun (whilst not negotiable as possible) is the best way to get them moving. Don't be put off if it doesn't happen over night either!
I have recently realised I was doing all the cleaning up (cos it was faster and the way I wanted) - DD told DH that it was 'mummy's job' and I had a real rethink. To start off we have had a big clean out.
Room by room so all the inappropriate/broken stuff has gone, sets are sorted and together and everything has a place (or at least room for everything, lol).
Now we have 'clean up time' when music goes on and we dance around and clean up, also have used a timer and harnessed DD1's need to win by having competitions!!!
Keep at it and you will see results but don't be put off in the mean time - last weekend DD1 cleaned her room all by herself as a surprise!!!!