I'd get very strict with them, sounds like you are very soft, sorry if I'm wrong.
My routine if I were you would be this.........
6.15am - get up, showered, dressed and a cuppa
7am - wake children if not awake, if awake make them breakfast while kettle boils.
7.30am - 8am everyone washed and dressed
8.15am hair to brushed and put up then gather stuff to leave the house.
8.30am leave for school (may need to leave earlier but I don't know how far school is) drop the 10yr old first, then 8 then 4 or you could rotate so that the 10yr old isn't late everyday? or get a childminder to take the younger 2, it shouldn't cost a lot and would take a lot of pressure off you.
9.15am - have a cuppa and write a list of work things that need to be done today.
9.45am - work
12.30pm have lunch and put something in the slow cooker for dinner (if you haven't got one then do get one they are fab)
1pm - work
2.45pm do the school run
3.30pm everyone in and a quick drink and piece of fruit.
3.45pm - homework older 2 at the table younger one in living room with you doing reading, the older ones can ask questions but they need to do their own homework so encourage them to think for themselves. No arguements, if they do well they can choose what they would like to do once homework is over.
4.45pm - sort dinner out (maybe boil some rice or pasta or potato to go with thats in the slow cooker) or some days do a quick dinner like pizza or pasta sauce or jackets pots (remember to put the pots in the oven just before you go to the school run or when you get back if you want a later dinner)
5.15pm - dinner time, sit together, chat about the day etc
6pm - bath time/ wind down time for 4yr old, perhaps dad can read a story while you tidy the dinner mess or vice versa, maybe the older kids can help.
7pm bedtime for 4yr old and wind down time for 8 yr old and 10 yr old if you like?
7.30 - 8pm bedtime for 8yr old, once she is in bed you do some work. Tell the children in bed that if they get out of their room or mess about you will send them to bed earlier tomorrow night.
8.30pm bedtime for 10yr old.
at 9.30pm or 10pm STOP chill, go to bed 
If your children do get up in the night put them straight back in their beds. Explain to the older children during the day what is happening and that they need to follow the rules and set an example to their younger brother.
10yr old being worried at night I would reassure and tell her things always look better in the mornign and it is bedtime and you love her - I don't know her but I would guess this is an attention thing? So try to plan something each weekend that allows you to give each child some one to one time.
I think the problem is that you are constantly play catch up and you are exhausted and who could blame you, they are running in circles around you imo, you are the only one who can stop this, with the support of your dh.