I am thinking, I would focus on one thing each day. So day 1, take all the outstanding washing/ironing down to a launderette and get it sorted by someone else, Meanwhile do a bit of a clothes and linen cull to make space for it to be put away easily when it came back. Do a charity shop run, and then you've got that side of things sorted. This can all be done with kids around ankles if you really need to. Or perhaps you could arrange it on the phone, and a neighbour could help you with dropping stuff off/picking it up?
Then on day 2, make it paperwork day. Buy some folders etc and make a big pot of tea, and line up envelopes, stamps, bank statements, pens, cheque book, laptop, staples and paper clips. Then stick all outstanding paperwork in a big box and apply the one touch rule, deal with each piece of paper in turn only touching each piece of paper once (anti procrastination measure). Deal with all bills, forms and so on as soon as you come across them. Make a pile for filing, and have a bin bag ready too for things you don't really need to keep. Then get into a rhythm - file, pay bill, throw, file, pay bill, throw, That sort of thing. Once you have tackled it, make sure you do it every Sunday evening ready for the week ahead. It will never be too bad then.
On day 3, I would sort the living room out a bit to make it a pleasure to sit in there. I posted a blog link that tells you how to do that.
On day 4, I'd do the same for the kitchen - make it nice to cook in, make sure all the basics are well stocked up and the cupboards clean and tidy inside and out. Perhaps book a professional oven cleaning service?
After that, you could focus on the kids' rooms one at a time, culling toys and clothes as necessary so they don't possess more than can be stored easily. Finally, make you own bedroom a lovely retreat.
For organisation porn, this website is easily browsed through while watching TV, and there are literally hundreds of ideas for little projects that make running a big household easier. www.marthastewart.com Things like numbering hooks, storing coats, grouping items and lists figure quite prominently.
Finally, have a big diary in the hall and a big basket for incoming paperwork so it's all in one place. Also we have a lost property basket at the bottom of the stairs and all rogue items that are not paperwork go in there. It's rare we can't find anything.