Some parents expect the world of one kid, while letting another sit on their rear end for years and years. It’s one of those double standards that usually has no real explanation. Maybe the hardworking kid is naturally more predisposed to being hardworking, and the lazy kid is the same way with being lazy, but that doesn’t explain the bad parenting. In that situation, the parent should let the hardworking kid do their thing and do everything possible to help the lazy kid overcome their laziness. If they push the hardworking kid to their breaking point and just the lazy kid fester in their ineptitude, they are doing both of them a disservice. 

Even if they are now officially adults, kids should not have to support their parents and siblings financially. That is the parents’ job, and a parent who cannot run the household without the constant labor of one of their kids is not doing their job well. It doesn’t matter if they have a child willing to work day and night for their family; this expectation shouldn’t be placed on someone who isn’t a parent to their siblings.