Assuming they're not both just figments of Ladonna's baroque imagination...her other brother is Gussie, and her sister is Madison.   Both of them appear to be in their teens.

Madison shows up in "Based on a True Story" in one of Ladonna's tales about an alligator sneaking into their house, and then later to take Bud somewhere or another.
Gussie is only briefly mentioned in the same episode.  He supposedly worked at an alligator sanctuary.