Complex sentence: The Old Catholic Churches reject the doctrine of papal infallibility; thus they reject doctrines which have been promulgated in the Roman Catholic Church by such means e.g. the Immaculate Conception and Assumption of Mary.
Split into simpler sentences: The Old Catholic Churches reject the doctrine of papal infallibility. Thus they reject doctrines which have been promulgated in the Roman Catholic Church by such means, including the Immaculate Conception and Assumption of Mary.