UK Visit Visa Process from Pakistan for my parents

Dear All,

I have a quick question and would greatly appreciate if someone could please help out...

My brother is a British citizen and planing to invite our parents from (Islamabad) Pakistan to UK on a visit visa for the summer.

Could someone please advise what is the minimum period visa can they get from the UK high Commission Islamabad ?

What is the process to apply for the visa ? Please explain in detail if possible, I am very new to UK visit visa process from Pakistan...

Is there any online process or paper based ?

Thanks in advance guys...