For those waiting. My mother-in-law adjusted her status in 3 months and 1 day. Interview was a breeze, lasted less than 15 minutes.
They did not stamp the passport though. Said that the stamp is not secure enough, and the card should arrive in 30 days. Should travel be required before...
There is nothing disturbing about it. Servanos committed immigration fraud when they received immigrant visas as unmarried children of US citizen parents. They did it...
Not only should you not apply I-130 before their entry, it may be a good idea to wait at least 60 days after their entry to apply (based on 30-60 day rule). Doing otherwise will make their application for admission to the US fraudulent, i.e. having immigrant intent while entering as visitors.
Your parents attained LPR status after your 21st birthday. They can sponsor you to immigrate in Family Based 2B preference category with waiting period of 9 years. See http://travel.state.gov/visa/frvi/bulletin/bulletin_3827.html
You'll be better off (at least faster) immigrating on your own.
It will depend on the time interval between an application for extension of stay (I-539) and an application for adjustment of status: 0-30 days is not safe, 31-60 days may be safe, more than 60 days is safe. It has to do with possible misrepresentation at the time of filing for extension.
It looks like the only way for her to get to the US is through immigrant visa. Her B-2 visa is most likely cancelled due to overstay, or will be if she tries to reenter. Her chances to obtain new B-2 are nil due to her immigrant intent.