First and foremost, he had to consider the kind of guests his son-in-law would have. The mother-daughter trio might shoot their mouths off in front of those upper-class elites. It would be an absolute disgrace to their family.
He really did not want them to spoil this important day for his daughter, but they were invited in the end.
It would be difficult to explain the rationale for not inviting them to the engagement party when they were technically part of their family. Gossip would abound if others were to catch wind of this.
It was Mu Yazhe who finally put down his foot.
Inviting them along would not pose a problem. What he would do was segregate them from the important guests in another plane cabin. During the engagement party, he would arrange for them to sit far away.
The man also knew that the three had loose tongues and were quite a handful, but not inviting them along would be showing lack of propriety on their part.