SOLVED. Middle-grade novel with mostly blue cover with a jar of fireflies on the front. About one kid who helps a group of siblings [s]

[Abby]

•Middle-grade novel with mostly blue cover with a jar of fireflies on the front. The copy I had was paperback.
•About one kid who helps a group of siblings (possibly orphans) I think?
•Title was something like keeping the [insert family name] or saving the [insert family name]
•I got it at the scholastic book fair sometime between 2010-2014

[Mai]

This one that came up searching WorldCat doesn't fully match your description but just in case! The cover is blue and it has a jar but there are kids inside, not fireflies.
Keeping Safe the Stars by Sheila O'Connor
"Pride, Nightingale, and Baby Star are spunky, independent, and orphaned siblings with only their grandpa, Old Finn, to care for them. That is, until he falls gravely ill and must go to a hospital far from home. The Stars must take care of themselves, but staying safe and keeping the outside world at bay proves to be more difficult than the children imagined."

[Abby]

That’s it!! Omg how am I just now seeing this