Beautiful children, RM!
I have two also, my son is five, and my daughter will be three in August. Having little children can certainly be exhausting! It does get easier as they get older.
That being said (and I offer the following as my not-so-humble-opinion), it sounds like your husband still wants to be a boy instead of a man. I know when my wife and I had our first child, it took me a while to adjust to the role. And my brother-in-law went through a similar thing. Having children changes the whole dynamic of the relationship. But he's got to step up to the plate as a husband and a father. I don't find your desire for help -- with the household and with the children -- unreasonable at all. Now, my wife stays at home, so she does do more of the laundry and cleaning. We also have a cleaning lady come in every other week to do give the house a thorough going-over (we had her come weekly when my daughter was younger). I help prepare meals, clean the kitchen, give the kids baths, and do the outside chores. Plus, I spend a lot of time playing with the kids on evenings and weekends, so she has a break. For the most part, my personal time comes after the kids are in bed (I went to the 10:00 p.m. showing of Matrix: Reloaded last night! ;o)
Your situation is a bit different, because you both work. Can you afford to have a cleaning person to help out every once and a while? With both of you working full time, it only seems fair that he more evenly split the household chores with you. I agree with an earlier poster about not worrying about the house getting messy. Its just not worth taking the time to try to keep it straightened -- that's time better spent relaxing, playing with the kids, or spending time with your husband. So let things go if you can (maybe keep one room neat and toy-free, as a sanctuary from the chaos!).
Where are the kids between the time your husband gets off of work, and the time you come home? I have to say it sounds odd to me that he'd be over at his mother's house every afternoon. If you are paying for child care during that time, you could save some money by having him care for them, and use it for a cleaning person. No reason dad can't help out here. I think a little personal time for each of you each week is good. But (IMNSHO, again) eight hours seems excessive -- three or four seems more reasonable. Do you get any similar free time for yourself?
It ain't easy when the kids are little. My wife and I are both stubborn and strong-minded, so we have our share of disagreements! I wish you well, and hope things improve for you.