Visitor visa for sister and mother

[quillnquire]

Hello,

I am applying for a visitor visa for my sister and mother. My sister is employed and my mother is a homemaker. My sister plans to show her bank statements, payslips, and a letter from her employer; my mother is showing her property documents. I have also sent my invitation letter that includes both of their names. My questions are:
a. Should they be applying in separate applications?
b. Are there any other documents that you would recommend I should attach?

Thank you in advance.

 

[Copingwithlife]

Separate applications
The invitation is only a small,repeat small part of the application. They have to show ties to their home country, travel history, finances .