Sister filing has nothing to do with his Legal proceedings, all it basically does is show the sibling relationship and out him in the queue.
Staying or not depends on the Asylum claim.
Sister can on;y file for Brother, spouse and children come into play when the PD is current which will be no time soon.
It does not have any current benefit, however no harm and you never know so do it.
I know the QR does not have to be and I could not think of a reason why it would not work.
Do not remember ever seeing one.
Probably a very unusual combination.
I have never seen a I 601a filed as a waiver for a Work Visa, my first thoughts are that assuming possible it would need to be an EB, which is very tricky to get unless the OP is exceptional and which also would question why he is here if he has such an opportunity.
Otherwise if the OP can chill then can chill presumably for ever.
USC needs to file taxes, and I would suggest do something to show Domicile, DL, register to vote etc, London seems to be lenient
Safest thing is to get a Joint Sponsor.
One is going to Canada I thought and anyway as far as the Consulate is concerned what Daughters?
It seems financially she is dependent on her husband, does she not work?
I get it I really get it why she wants to come to the US.
Not sure I understand why she would want to go back to Pakistan. I doubt the Consulate will either.