Family traveling to Frankfurt and will travel to the Ronneburg Castle as that is where my German ancestors congregated and then immigrated to America and then the Amana Colonies in Amana Iowa. Looks like a train from Frankfurt to Langenselbold would work?
Ronneburg is a bit difficult to get to with public transportation, but I would go to either Gelnhausen or Büdingen by regional train from Frankfurt. This gets you closer than going to Langensbold.
Wonderful, Staufen castle and if you are there when they have an event, like their medieval Xmas market or Easter market, it is well worth going there. There is also a falconry there and para-gliding.