I would say definitely come out to your aunt. It's good to have someone who can support you if you somehow get outed to your parents. I personally wouldn't come out to them in your position, but that's more of a thing for you to decide. Normally I would say not to at all, but your aunt changes things a bit.
#advice
fickle turretBOT
I honestly don't know. Maybe just bring it up yourself when you're alone with her. I'm really bad at giving advice on how to because I am basically in the same situation but minus a family member who will definitely support me.