On the parents:
http://ukba.homeoffice.gov.uk/partnersa ... relatives/
They qualify on age as one is over 65 - however, the financial test isn't passed - they need to be largely dependant on their child and have no relatives around who can take care of them.
Alternatively - they could qualify on their own merit under the tier system.
The final option here is for her to move to another EU country and exercise her treaty rights for 6 months. She may, and I stress may, be able to bring them over under the EU family permit - she could then return to the UK under the Surinder Singh ruling.
But even then - they would apparently need to be dependant on her (
http://www.ukvisas.gov.uk/en/howtoapply ... s#23094897) - and that means financially. Since they are supporting themselves, then that route is probably closed.
On the sister. Simple answer - not as your friend's dependant. It would have to be on her own merit.
So - the long and the short of it is "no" unless they qualify in their own right for another visa category - which are wide and extensive - so she'll need to do her own research here.
M.
