I think it incredibly sad that several posters have to ask how the OP's situation might be tough on the children.
Do you not think it is hard to watch your parents split up? I don't know the circumstances of the OP's aunt, but with separation the children may experience:
antagonism between the parents, use of the children as "pawns" to hurt each other, seeing one or both parents a lot less, shuffling between homes, financial hardship, moving, and the introduction of new boyfriends/girlfriends.
Now times this by two or three. How incredibly stressful for a child.
A lot of you are saying, "life happens." If that is the case, then this woman has been incredibly unlucky - but much more likely I think this woman is not good at picking suitable partners, and is not learning from her past mistakes. And her children will suffer, because they do not have stability, do not have contact with their fathers (except for the youngest two), and are "raised" by a man who prefers the children he fathered to the rest. Perhaps they are well fed and clothed, but that does not make up for a broken home.
Hence my earlier comment about boarding school perhaps being a good place for them.