My sister has left her two kids with our Dad, who has left them in my care since he works. Both Parents have been gone for nearly 6 months. I read that abandonment requires intent on not returning, and she shows up every couple months just for a couple days and then takes off again without a word. Both parents have a history of drug problems and Mom has a record with little stuff(mostly juvenile) and 1 felony. Any advice on what to do, where to go or who to ask would most helpful, thank you.

I don't know what you read, but please see the sticky note on abandonment at the top of this forum. You will see abandonment is not the issue here.

You need to define what it is you want. Is it guardianship, custody, adoption, or what?

You should have applied for guardianship immediately as you need the legal right to sign for medical care and other legal stuff.