Thank you for posting Dano3456. It is a fact that Jehovah's Witnesses split families. Most on this site have experienced it, it is not rare, it is normal in JW circles.
They may seem like decent people and probably are but they are under the influence of others, namely the governing body of their religion -- although they will deny it because they don't realise how they are being controlled. The JW religion ticks every box qualifying it as a cult. JWs will put obedience to these men before anything else, imagining that they are doing their duty to God. This total obedience means doing things such as punishing members of their own family by exclusion should they choose not to be a Jehovah's Witness.
If you value your family, clear thinking and education, self expression and personal development, have no more dealings with this other family and most especially don't let your own children get sucked into their way of thinking.
I am not being too alarmist but already your children sound like they are taking their 'friends' ideas on board.
The antidote is to discuss with them the importance of only believing things which can be proved by evidence. The Bible is not evidence by the way. None of the beliefs of Jehovah's Witnesses past this test.