It never ceases to amaze me how "getting along for the kids" always, and I mean always involves the woman tying herself up in knots to accommodate dickish behaviour from her ex. The man is NEVER involved in making things easier for the kids. He just does whatever he wants and if the woman makes a fuss, she is "making it difficult for the kids."
Stop. Stop right now. The point is that it is NOT easier for the kids. He is around all the time and that's probably confusing. You are seething with resentment and they probably feel in the middle.
Instead, if you can't get him out, absolutely go with calmly making it clear that as you're separating, you're going to act accordingly. Absolutely NO laundry. If you can ditch the cooking, do so, although I can see that being tricky as the kids might ask why you're not feeding him when he's sitting right there. But absolutely no need to go out of your way - ie no buying his favourite snacks, no making tea/coffees etc etc.
If there's anyway you can convince him that you need to act as if you are divorced and therefore he's responsible for him and the kids on the days he'll have them once he moves out, that would be great. But assume that won't happen. At the very least, feel free to just tell him that on the basis that you're now sharing access to children, you'll be going out every wednesday and it's up to him to sort kids on that day. Make sure that your weekly shop is done on a thursday....
Do not allow him to take over the downstairs. If he won't go into the office, that's on him, but you and the kids do not need to tip toe around him. Sit down and watch tv, do the vacuuming etc. If you want to be super sneaky, do it just two days a week then you can innocently say, "I thought Id have access again twice a week while you were at work and have planned accordingly. If you're not going to work well, what can I do?" I'd definitely be getting kids friends round for the half term.