Green Card through Brother or Sister
See clip from Attorney Rajiv S. Khanna's conference call video that addresses this question.
That category takes 13-14 years. During the time you are waiting for your priority date to be current, you cannot stay in the USA just because your green card is pending. You can, however, stay or come to the USA under a visa independent of the green card such as L-1, H-1. You can also apply for a green card in several categories simultaneously.
Continue through your sister. That seems to be the best option. Brother's application can stay pending. It need not be withdrawn.
It will be faster for her to petition and she can do so as soon as she wants. I would suggest she should apply when she moves to USA. If you wish, you can also start a petition for your brother. He can wait in more than one category.
You cannot petition for brother until you become a US Citizen. And, even after that, it takes over 10 years to get a green card. See family category 4 in the current visa bulletin: http://www.immigration.com/visa-bulletin
Check out the Form I-130 filing fee.
You can withdraw the Form I-130.
You can simultaneously file through as many green card categories as you wish. Check out the backlogs on the visa bulletin.