When one of Jehovah’s Witnesses does something that his local elders deem a serious offense against God and Watchtower, he will probably be disfellowshipped and therefore shunned by other Jehovah’s Witnesses. When I say that he’ll be shunned, I don’t mean he won’t get any presents on his birthday or that he won’t be invited over for Christmas. I mean that he is dead to them. In most cases, the Witnesses will simply pretend he’s invisible (like that episode from the Twilight Zone) and many will simply wander off if he attempts to communicate with them in any way. Either that, or they’ll get angry and blast him for it.
They call it “congregation discipline.” When they speak of it, they make it sound like it’s a punishment from Jehovah God himself. In reality, the decision to disfellowship is made during a closed-door session with three local elders. It’s how they keep their followers in line.
So how does it work and how far does it go? Technically, people living in the same household aren’t required to shun one another or expel the wrongdoer. But I know of many cases where the local elders did pressure parents to kick out their adult (18 years old+) children even if those children had no where else to go. Since good Jehovah’s Witnesses are supposed to obey their elders, this can put the parents of the disfellowshipped person in a tight spot. So while the elders can make it hard for the family, at least they do have the right to say no to the elders. That’s mostly because the Society hasn’t made expelling family members from the home mandatory, even though shunning in every other respect is mandatory.