If there is any way that you can afford it, hire a cleaning lady!!! If not then I knew someone who did Sat cleaning, the whole family had to do it, it was done in the morning, nobody went anywhere or did anything unless it was done. You can put the jobs that need done, on papers in a jar, and everybody pulls one and does one every day.
My son is 14, I feel your pain!!! You have to set strong limits, no phone, tv, video games, computer, etc, until all the homework is done. He can do it between school and home (where is he at that time). You can have them help you with dinner. My son has to set the table, clear the table, and put the dishes in the dishwater and empty the dishwasher, his other duties are to feed the cat and dog, and take out the trash and do whatever else I need done. Both of your kids are able to do work.
I would also be careful not to put too much on them. You are stressed when you get home because you have so much to do, don't start stressing them out too. Tell them they can do homework while you are cooking dinner or between 7 and 8. Or something like that. Give them a choice, even kids need a little time to wind down after their day, it sounds like they are just as busy as you.
Put dad to work. These aren't just your kids. Don't nag though, sit down and talk to him about how stresed you are, and ask him if he can take out the trash, or whatever, start with one job and give him lots of praise, then you might find that he is more willing to do more. Sounds silly but so far it is working for me... read "Mars and Venus: Together Forever"