Famen Temple and Qianling Tomb are far away from Xian urban area. They are in the different direction. Famen Temple is in the west to Xian and Qianling Tomb is in the north to Xian. It needs a whole day to visit both of them. Also, as you will take train from Xian to Luoyang, it's too rush to visit either of them. Usually, the train K618 leaves at 1533 and you need to be at the railway station before 14:00. Try to adjust your itinerary.