They were both their daughters and they were twins. So, for parents to be bias to this extent, was extremely shameless.
But, Xing Lan was also someone that had embarrassed them. So, the two elders avoided their daughter like the plague. To be exact, they kept her under surveillance. Because, while they avoided her, they were also afraid that she'd do something even more embarrassing.
Hence, no matter how Li Can treated her sister, the two elders did not think it was wrong. In fact, they felt that Li Can was very thoughtful for taking responsibilty of Li Xin.
The elders had been living a luxurious life because of their songstress daughter, so they couldn't allow someone to ruin it.
As soon as they heard Li Can say that Xing Lan was participating in a competition, the two elders felt their hearts tighten.
Xing Lan explained her situation with her parents to Lin Qian. Since Li Can had begun to cause trouble, her parents were definitely not far behind.