The fact was that the Princess Ling Meng hadn't anticipated that the three princes would follow the Emperor. Shockingly, their carriages had travelled on the road side-by-side and had kept bashing sideways into each other. Luckily, this street was wide enough to accommodate them. Otherwise, perhaps even the houses on the side would have been affected by the three, and would have collapsed.
[I still don't know what father aims to achieve by this plan of his. Could it be that he is not satisfied with the usual infighting, or does not consider it fierce enough? Would he have those three compete, expose their weaknesses, and humiliate themselves in front of everyone? With my three elder brothers' current behavior, this is not entirely impossible!]
However, the scene that the Princess Ling Meng had just imagined would not come true.