After reading through the comments and tinselcat pointing out the leaching part it reminds me off my ex and I moved to an entire different country and he still haggles my family from my sister to congratulating my mother in shop on the birth of my baby :/ I'd say gtfo while you can and while that type of person hasn't managed to leech on to someone else close in your life so it's harder to get rid! I would seriously move schools and not be bothered if it would freak me out that much!
That part where Russellm says she gets snappy reminds me of that vid going round fb where he tells a joke about telling his teacher to mind her goddamn mf business!
But that's what it comes down to it, there is no reason for you two to hang out your daughter doesn't like her or her son and neither do you so just tell her, I don't see the point why we should hang out!