maybe a few laundry baskets, one for whites, lights, darks, baby things. (outside the bathroom, maybe?)
so the three eldest have to put there dirty laundry in the right basket.
and when the clothes are dried and folded they put them away themselves.
the two eldest can iron their own things. and only iron school uniform for the 9year old.
they can also change their own bedsheets and keep their rooms tidy. (their room = their responsibility)
try to throw out junk mail and envelopes and leaflets that arent needed straight away. only leaving you with the important bit of paper, i.e. bill/letter (i had masses of paperwork everywhere and 90% off it ended up in recycling bin).
couple of big tubs/boxes for chucking in babies toys at the end of the day.
for everyone, no eating upstairs, and put dishes in sink/dishwasher themselves after using. (saves finding rogue moldy cups and crumbs under beds!)
box at the bottom of the stairs for bits and bobs that need to go upstairs, and then every time you go up take something with you.
hope you find some of the above useful.
oh and cut yourself some slack! you have enough on your plate.
goodluck