My wife and kid trip consists of air part (using airplane) and Deutsche Bahn part (by train). So they will arrive to Frankfurt by plane and instead of waiting for almost 5 hours for the train part I'll pick them up at airport.

Is it possible for us to cancel that second part of that trip (because connection time between "flights" is too big) and reimburse some part of that price? What should be the entry point for it - Lufthansa or the DB?