Hi Ohwhat
I have 4, and D5 is due in Nov! Mine are a bit closer together than yours (oldest is 6) but I can sympathise! I find the hardest times are, as you said, when the older ones have planned activities, and have to drag all the others along as well. Am hoping this will get easier as they all get older?!
I also find the after school hours hard, but as long as we stick to a tight schedule we are usually ok - ie. tea for bang on 5pm, then bath time, bed time for youngest 2 by 7pm, ect. DH doesn't get in from work until 6:30pm at the earliest so I'm also on my own for most of this time!
Weekends - DH has no choice but to help out. There is no way I could manage everyone doing stuff without 2 of us chipping in. We often split up, so the older 2 go out and do some stuff, especially while the younger 2 are having naps ect. We do try and do something all together at least once during the weekend (eg. go to the park ect) even if it's just for an hour. I sometimes get one telling me that they don't want to do x, y or z, but I usually just ignore this! In a family of 6 (soon to be 7!) they don't get a choice all the time....and I think it is good for them anyway to appreciate that they have to sometimes do things that other people would like to do, and not only think of themselves. Also second having friends in to play...it is often easier for people to come to us, as I have so many to organise, especially if it's during the week when DH isn't around.
I really think you need to get your DH more involved. Could you not have an agree time which is not kids time? Realistically though they are his kids as well. Although my DH moans some of the time about stuff, but I pretty much never get time to myself, but when we decided to have kids, we made that decision? They are not little for ever....
On the behavior side of things I have a chart for my oldest 2 - bad behaviour gets a cross, and for every cross at the end of the day they have to go to bed 10 mins early....works a treat with mine! The threat of a cross is usually enough to stop them doing whatever it is...
I think you just have to also remember that there are always positives to any negatives....although it's very busy with 4 or 5 kids, and they might not always get to do lots of activities, at least the kids always have someone to play with! I have friends with only 1 DC who moan as their kids are always lonely - mine can never complain about that 