Hannah Montana Question?!?

I dont really like Hannah Motana but anyways one day i was watching this episode and it was the one with "Aunt Dolly and "Mamaw". And it seems like they are the same age since their talking about fighting over the same guy. I thought mamaw was Robby Rays mother and Dolly his sister so how an they be fighting over the same guy and calling themselves names...can someone help me with my confusion?!?