These are things you can say to your children to try to make them stop fighting and teasing.  Good luck!
Teasing:
- It is not nice to tease.
- It is not nice to tease your little brother/sister.
- It is not nice to tease your friend.
- Do you like it when people tease you?  No?  Then you should not do it to others.
- Teasing makes people feel bad and is not nice.  You should be friendly instead.
- When you tease someone it makes them feel bad.  Do you want them to feel bad?  Why?
- Stop teasing your brother/sister!
- If you don't stop teasing right now, Mommy will take away the television for 2 days.
- Why are you teasing your brother/sister?  
Fighting:
- Please stop fighting.
- Please stop fighting now.
- Stop fighting!
- No more fighting!  Enough!  
- I want you to stop fighting.  You are family.  Families should not fight with each other.
- If you love someone you don't want to fight with them.  
- If you don't stop fighting now, Mommy will take away your toys for 2 days.
- If you keep fighting, Mommy will not take you anywhere.  Next time you want to go to the toy store, Mommy will not take you.
- Enough fighting.  Please tell your brother/sister that you are sorry.
- Look!  You made your brother/sister cry!  Please tell him/her that you are sorry.
- Saying sorry is a nice thing to do.  Can you show me that you are nice?
You should print these out and carry them with you.  If you take out a piece of paper every time you want your children to listen, they will quiet down every time they see you begin to take out the paper.