I heard it rom an inside source that although Kerry hasn't the slightest idea how to raise her kids, she does care about them a lot, she just hasn't the faintest idea what to do with them. The nanny is a family friend who's been around since before Holley and max and she may be reluctant to leave them as she's the only stable influence the kids have. Apparently the younger of Brian's girls is a nervous wreck, and as a nanny myself I'd have never willingly left a job if I thought it would damage the child.
Also, my mother was a radio journalist back when Kerry and Brianna broke up and she interviewed him. He compared the children to puppies and admitted it was a mistake to have them. The listeners gave him a right bollocking and he fled to oz not long after.
Kerry had such a terrible upringing that its not really surprising she doesn't know how to be a good parent to her own children. After all, we learn from our own parents example and Kerry's mother was next to useless passing her from pillar to post. She had no stability at all. Is it really any wonder she's as screwed up as she is? I don't doubt for one second that she loves her kids but because of her background she doesn't know how to mother them correctly.
Brian is an absolute waste of space though and I would even go as far to say that he is responsible for a lot of Kerry's problems because for all her sins she was madly in love with him and had in marrying him the kind of family life that she'd always craved. When he left her and ran off with another woman he broke her heart and that's when most of her "troubles" began.
He makes me sick. There are people in the world who can't have kids and then you have losers like him who breed and then can't bothered with the kids once they are born and they realise how much hard work they are. To quote Jeremy Kyle "stick something on the end of it!"