Ronsberg is now Pobezovice town in southwest Bohemia. Unterhutten is Dolni Hut in same district. Dolni Hut was little village near German border. It was destroied in about 1950. It was part of parish Rybnik.
Parish registers of both parishes are deponied in archives in Plzen. Unfortunately they are not online. You need to search them yourself by visit of Bohemia or you can hire some of Czech researcher.
All the best.