cats are possibly getting to grips with each other

What does 'getting to grips' literally mean? They are both annoyed with me apparently, or at least keep approaching me separately with problems they can't articulate. Nancy got up on the shelf and knocked some things off, including a candlestick which broke, but might be fixable. I looked at some pictures of her from four or five years ago and I have to say, she is probably overweight. She and Helmi have had negative interactions at least twice tonight (it takes the form of Helmi running at Nancy and the two of them scratching the air between them with one paw for a few seconds of 'bring it bitch'.