Okay, I will jump in here.
I see that some posts on here are getting picky and not going in the best direction!!!! This isn't about young students being put in a position of having to support themselves.
I realize that I have experienced a similar situation.
VERY similar.
I have a sister with 3 kids.
At this point, the situation is pretty darned bad...
The kids (two are now adult 18,20, and one teen) do not have adequate clothing, are not fed healthy, do not have jobs of any kind, at all.... are not being given opportunities to prepare them to become independent responsible adults.
(Just in comparison... which I know I really shouldn't compare... My son, just 14 now, has a sizeable savings account of his own by doing great neighborhood lawn work. Quite a bit of money! Okay, I know, braggin' a bit... but def. not taking the credit or claiming any superiority.)
The hard truth is that in most of these cases, people find themselves in these situations because they choose to keep finding themselves in these situations. They don't want to make the hard decisions necessary to live their lives in a way to insure better. They don't want to take ownership... They also don't want to feel 'judged'. (notice the judgement in the OP's post)
At one point, myself, and other siblings, have wanted to help... But have realized it is to no avail.
In her case, she (and her husband) have not stepped up, and have done without, and have not empowered themselves... AND THIS IS EXACTLY WHAT HER CHILDREN HAVE LEARNED. It is a very well known thing... Learned Helplessness.
Any help that would come with conditions, strings, or judgement/opinion, just would not be accepted. Strict freebie handouts only. (Of course, those would ALWAYS be just a little too welcomed....)
I do not know the backstory in the OP's situation... But, something tells me that there is more than a simple 'hit some hard circumstances' going on???? something tells me that there is more to this than meets the eye. Especially since the OP has not been aware, and is suddenly 'surprised' by what she is seeing.
OP, I really don't know what to tell you... In my case, my neice and nephews are are young adults (one older teen) and I don't feel like there is really anything I would have been able to do to change where they are at. If your sister has not been forthcoming, and has not been trying to help herself, by possibly opening up to you and 'letting' you help her to help herself... there may not be a lot you can do.
I know how the situation feels. ( not good! )
But, you can't let yourself harbor any anger or judgment.
That just will not help.