Nagging will always happen in our house, since one of my kids
has ADHD and you have to tell him something 42 times before it gets
through.
We recently heard of something called the Family Pact, and put
it to use in our house. It's made a huge difference in yelling. You
and your kids make a pact in writing to respect one another (no
yelling, hitting siblings, ignoring etc) Anytime the pact is
"broken" the person (child or parent) has to apologize and do one
nice thing for the one they broke the pact on. It could be anything
from helping on a chore, writing a letter, draw a picture, etc.