I work 4 days per week and there are times where I do not feel like I am coping as well as I should.

Essentially I try to simplify things. I limit the extra activities for the children, so they have 1 thing each. Earlier this year DH had DD1 enrolled in twice a week martial arts and it just about wrecked me, so I pulled her out the moment the contract was up.
I limit my activities, whilst it sounds great to be doing yoga, meditation etc, the stress involved in getting there, making sure DH was around to look after the kids, the loss of time at home to do things or just plain rest, was not worth the benefit.
I insist on have a home day once a week, a day where we go no where. We live just out of town, so just a quick trip means at least an hour of the day gone. I find those days beneficial, I just take me time doing what needs to be done in between doing those things that I need to do.

I don't tend to feel guilt these days, as I feel the girls having a roof over their head, good food on the table, being able to not miss out on school trips etc, is important. We would struggle to provide those things if I was not working in some capacity. Plus the stress of lack of money for me is worse than the stress of trying to do so much.

Check out the book "A pressure cooker saved me life". Written by an Aus news-presenter, who did try to do it all till her body told her to stop. She had various tips in there for coping (some are good, some not so) , along with some history of house keeping (very interesting), lots of pressure cooking info (great, as I don't have time for slow cooker prep of a morning). Really, just reading her story I found beneficial.