Parents want 20-year-old daughter to move in with 24-year-old brother because they don't trust her to live independently, don't understand why brother refuses: 'I live with my fiancée and while we do have a spare bedroom, my fiancée is 4 months pregnant'

An older sibling should never be fully responsible for their younger sibling. 

"Parentification" happens all the time, and we should try our best to stop it in its tracks. This is when parents rely on/force their older children to take care of their younger children. They force them to take on the responsibilities of childcare while they're still children themselves, which ends up impeding everyone's development. Maybe the parents do it because they see it as a way to offload their duties, or maybe they're just absent and their children have no choice but to step up. Either way, it's unfair to the kids and should be called out when we see it. But it's all too common, and ends up putting the older children in difficult situations. Even when they try to branch away and make lives for themselves, the responsibilities end up coming back down on them. 

But this happens sometimes even without due cause. Like in this story, where the parents were so overprotective of their seemingly normal child that they made it everyone else's problem. Even though she was a regular young adult living with peers and attending school, they hovered over her every move. Even worse, they made her older brother hover over her every move. The brother was willing to comply up to a point, but when they started to ask a little more of him, he understandably bristled. He had just started to carve out an independent life, and he wasn't willing to forgo any of that.