Hi allaboutme,
I wrote all this before your second post, please ignore the bits that aren't relevant.
I work from home quite a lot and DP is a SAHD. Won't go through in great detail all the arguments evolution we have gone through but here are how we deal with it:
Fixed hours are the only way to go I'm afraid, however much he might fight it. Perhaps you could plan something to watch on TV or Sky Box Office, so it starts at a fixed time, but make it clear to him that you really really want to have your evenings together. Fitting his work to regular office hours is pretty vital tbh, you don't want him developing a porn/dirty den habit because he's sat on the computer for all hours. Playing computer games instead of coming to bed with you is not going to help him with "being bad in the mornings" and in the long term could become a problem for your sex life
You could also point out to him, if he's not being paid hourly, how low his hourly rate is if he works a 10-hour day rather than a 7-hour day.
If the work starts getting stressful he will find that being in a structured habit really helps because it's much easier to switch it off. When my work gets bad I think of logging on to the laptop as opening the portal to hell?.
Get an office-style flask (different to a travel one, not that it matters!). Get him to make a flask of tea and take it with him, so he isn't disrupting the kids when he pops down for a brew. (Mine holds 4 mugs worth!) My DD used to get upset if I went downstairs because she didn't want me to go back up. When she comes in from school I come down to see her, fill the flask, and go back up after 30 mins, and then she doesn't see me again till I finish at 6pm.
On a Friday, DP gets a lie in and I take DD to school and collect her, and work a bit extra to make up for it. It means he doesn't get stir crazy, and I get the chance to remember where the place actually is.
Losing an hour that you used to have to yourself is huge, and you should look at how to get it back ? perhaps in the evening you could start your evening an hour later than you used to, and take your pottering time while he finishes off? Give him an hour's notice to finish things off before your "couple evening" starts. Divide housework between you ? don't let him half-unload the dishwasher once a week and then get all pleased with himself for "doing his share".
I have no experience of being a SAHM but we have had to recognise that we each have fixed things to do ? his have fixed hours (get DD up, get her to school, collect her etc) and mine have more flexibility, but both are equally important. Your DH is treating the house a bit as though it's all his office and he can dip in and out regardless of what else is going on, which is not really fair on you when you have LOs at home.
Re the not getting the kids dressed in the morning, this needs doing and one of you has to do it. Explain to him that having a lie-in when nothing is done when you get downstairs is not relaxing and misses the point. I would set a routine so you get turns to lie in, and whoever gets up gets everyone dressed and does breakfast.
I know "you are lucky" is not a very helpful comment when you have a problem with something - but imagine if he was completely out of work. Sounds as though things have worked out really well for you both. You just need to make some adjustments to the household routine - and they include him adjusting to you, not just the great hunter-gatherer doing exactly what he wants when he wants it, while you buzz around fitting in with him.
Good luck