Dependent visa for parents and sister

Hi!
I am on Indeifinate visa and my brother is on Tier1 general in UK. We are 2 brothers and 2 sis. My parents and ond 1 sister are living in Pakistan. Other sister is married and living at far distance. Parents are 65 and sister is 23 years.
If i apply for permanent residence of my parents then my sister will be left alone.
What are chances that my sister will get indefinate visa alongwith parents.

Should i apply for premanent resideance of all three at same time or parents should apply first and then sister?

Please advise