My nephews were like that when they were little too. Now they are 19 and 17, and very nice guys...but thyestill bother eachother and fight, lol!

These are your grandchildren, Speak Up for their safety.
This is abuse. I would not stand for this in my family.

Looks like everything is fine for right now.When mother is at work she doesn't see what's going on in her own house only what's she's told.My husband and i are just visiting for ThanksGiving.I will be so glad to leave today.I live 3 hours away past Canon,City CO

Connie,
Try to speak to whichever parent of the grand-daughters is your child in private and at a time when emotions are not running high. Express your concern for the older child in a non-accusatory manner. Acknowledge that it is difficult to be a parent to teenage girls and that you know they are doing their best but that you wanted to make sure they realized what it looks like to an outsider.
Maybe they don't realize the dynamic that has take hold.

Do not say anything in front of your grand-daughters. That will cause far more problems.

And I agree with the poster that said you should offer a loving place for the older child to come to. She needs it.

My mother did the same with one of my brothers - always taking his side. That brother still doesn't seem to fit in with the rest of us as adults. She didn't do him any favors, but I'm sure she thought it was the right way to handle it at the time for some reason.

WOW! Brat and monster? Seems to me favoritism is shown here and maybe not by just the parents!

I re-read the posts from Connie and don't see the word monster anywhere.