I feel your pain, bro, on many levels. The modern lifestyle doesn't leave much time to organize a thought, let alone live a fulfilling life with adventures outside of kids and work. Trouble with SWMBO like this can make things seem unbearable. Instead of a loving family I sometimes feel like my SWMBO is more like a fellow employee I have to work with to get s**t done around the house.
Anyway, here's something that helped us in those times when every conversation it seemed to go south.
Counseling. We decided to seek counseling and it was great move. We found someone 5 minutes away who was totally cool and understanding. An empathetic and skilled counselor will help your spouse see and understand your feelings on this... and help you to see how she feels about it. I'm sure her perspective on this makes sense, once you can get an proper explanation. In other words, I don't think she thinks she's being selfish. There's some other way of looking at things from her point of view that makes it no big deal to disturb you at these times. My wife and I both felt like we were doing everything while the other person didn't do his/her share. Obviously, we couldn't both be right.
We also had moments like you describe that we couldn't seem to make progress on. Counselor helped a lot, bro. Plus, grandparents and friends are very cool about baby sitting to see a counselor for an hour.
Another thing to do, honestly is to find some more ways to have quality time with your wife. Not easy with the kids, I know, but I came to learn that part of the problem with situations a lot like you describe - no peace, ever - had to do with needing to get some quality time together. Even just sitting on the couch for 10 minutes with my wife and talking did wonders for all of these things...Plus, your sex life invariably improves.
I'd recommend the counselor. It helped us tremendously.
A second thing we did (my idea) was to stop dividing every chore up equally. I kind of like cooking so I took on more of the cooking. Made for much less bitching about the kids' laundry! Fair division of labor doesn't mean half. People have different capabilities.
Anyway, hope this helps and best of luck. SWMBO and I have gone through some rough times, but with some insight they give way to some truly awesome times.
Good luck, bro.