D.B.
From this and your other posts, it really seems that you are focused on the tiniest slights and you aren't seeing any joy or pleasure in life. You and your husband are unhappy, and while you separate, perhaps you don't do what needs to be done to heal your hurts and work on new ways to communicate. If you're not getting help from an objective source (counselor, therapist), then nothing is going to change.
We are all products of our upbringing, and I know nothing about yours, your husband's, your sister-in-law's or your friends. But there seems to be a whole lot of going around and blaming other people and looking for their screw-ups, instead of focusing the lens inward. You are profoundly unhappy, and that changes how you see people and how you speak to people. It also changes how you react to things they say or do.
Fighting over a post office receipt? Getting free child care and then being upset that your free sitter eats too much? He blames her, and then you fight with her? You are complaining about someone else's kids and upset about someone in the supermarket who offended YOU by taking some basil? You're not the world's police officer, you're not the world's expert on parenting.
I suspect you are having so little pleasure in life that the only way you can feel good is by showing that someone else is "less than" you. Perhaps you never were validated as a child, perhaps you never felt good enough. I understand that - I was raised the same way. It's a horrible thing. But I knew I needed better skills to have a good marriage, and I surely didn't want to raise my son to feel the same way. So I got help, and so did my husband. We went to separate counselors and also saw someone jointly. We stopped blaming the other one (or his ex, or my family, or his kids...) for everything and decided to work on what we could control - which was our own growth and our own attitudes. We've been married 34 years, have a 29 year old son who is awesome and whole and confident, and we learned how to "fight fair." I suggest you make the time to take care of yourself by finding out what makes you see the world the way you do. If you understand things better, you can make better choices. It really is worth the effort, and it's a gift you give yourself. Otherwise, you will be miserable, and you will raise 3 little kids to hate the world, each other, and you and their father. Don't do that to them.