What a bunch of poseurs your family is being exposed to. That's right, I said it! That's what people are that would act like this. They are nice-nice to your face, so long as they are allowed to indoctrinate your children against you behind your back. And let's not kid ourselves, that is EXACTLY what this behaviour is about......CULT recruitment.
After the threatening letters I would dumped them all like the manipulative, crazy, bat-shit cultists that they are. That was their TRUE colours right there. Everything you are seeing/experiencing right now is all for show.....glossing over how they really feel about you and your family in order to suck your kids into a controlling cult.
Wake up. You are being played for fools. I'd never allow my children around them alone - EVER.