You have lots of good ideas on here already and I would tell you what I would do. Give each kid a list when they get home and say you will be doing this or there will be no games tv phone etc. This is the time you have to do it in. Then ask them if they have questions. Leave them to it and check on them and encourage encourage encourage not yell n harp on them. Say your doing a good job Im proud of you then walk away or say I have a few minutes do you want some help? Just make sure you help and not get sucked into cleaning the rest of the room! :) If its a BIG disaster be reasonaable. It wasnt messed up in a day your not going to fix it in a day....well unless you save it for a Saturday or something.
Once the room is caught up and looking good give them a well done and now we are going to do these things daily and yes I believe in rewards every once in a while. You can figure out whats best for you 3 days a week every two weeks or once a month etc. Maybe it could be a coupon for some special one on one time with you, some cookies, spcial meal, some girly glamour (fingernail polish, hair accesory, earings necklace) Whatever you feel but I do think this helps and encourages them and lets them know you are watching them and know they are doing a good job. In between you have verbal praise.
I WOULDNT stand over them and tell them every move to make. They get to reliant on that and will not be able to make decistions for themselves because you usually tell them what to do. Just give em guidelines of what needs to be done and let them choose how to do it
Hope you can figure out so you can all be at peace.
M.
Ooo one last thing. They are kids and they arent perfect if you see something that is not as neat as you would like tell them it would look better if it was neater or say something like "I like the fact you hung your clothes but they would look better if you straightened them". Then show them how. Its going to take a while to make all the miner adjustments.