I send my 2 to different areas of the house if they are winding each other up.
I also walk away from alot of Dd3's iritating but not life threatening behaviours.
I choose my battles very carefully
I used to go in the garden and smoke but now I have given up I eat chocolate at night when Dd3 is in bed.
You are definitely not a bad mum, if you were you wouldnt care.
Be kind to yourself and good luck