Yu Shuisheng was not the biological child of Grandma Yu; he was brought home by the late Grandfather Yu.
Because Shuisheng was not of Grandma Yu's own blood, she had always given Wang Chunhua and her daughters cold shoulder, taking every opportunity to make their lives difficult.
While Shuisheng was still at home, Grandma Yu dared not be too blatant. But during the period when Shuisheng disappeared, Grandma Yu wished nothing more than to drive Wang Cuihua and her daughters to their death.
Jingting had told Suizi about this soon after she married into their family.
From the look of things, Shuisheng also seemed to know about this.
Otherwise, why would he lead Cuihua home immediately after returning, and stir up a fuss in the old Yu Family from top to bottom?
Since both parties knew they weren't related by blood and there was no kinship to bind them, they abandoned all pretenses of respect for each other.