The Untold Truth Of Hosanna Plath
The reason you don't see Hosanna Plath on Welcome to Plathville is very simple; she doesn't live anywhere near the rest of her family. As InTouch notes, the very first episode of the show revealed that Hosanna resides in Ohio with her husband, Timothy Noble, so appearing on Welcome to Plathville, which films in Georgia, where the Plaths live, wouldn't be feasible. Plath actually works with her husband too, as the duo performs music together with him on the piano and her playing the violin.
According to their website, the couple tours the country constantly so time would also be an issue. TV Shows Ace describes Plath as something of a musical prodigy. She released three solo albums before even meeting Noble. Plath was also previously a key part of her family band. She earned a scholarship to study music in college but instead opted to learn through practice and playing instead. Her parents described the decision as a "personal" one.