Complex sentence: Briefly after 1500, two members of the Keldermans family of master builders successively carried out a plan to expand and remodel the building into a cruciform shape, but only a northern transept arm would be added before fire and social turmoil brought construction to an end.
Split into simpler sentences: Briefly after 1500, an ambitious new construction phase began, successively carried out by two members of the Keldermans family of master builders. The plan was to expand and remodel the building into a cruciform shape, but only a northern transept arm would be added before fire and social turmoil brought construction to an end.