Hi Patty,
What a tough situation you are in! As far as your mother knowing, I would do as your sis and aunt suggest. If your mom asks, then that's soon enough to tell her, but I don't think she will.

Now in regards to the FMLA -- at my last place of employment one was required to use their sick leave, then their vacation, then unpaid --- in that order. It may be worth your while to check on that again.
Take good care,
Okie