If was applying my sister and brother and their families to the US in 2006, how do I sponsor them once they approved?

The April, 2017 Visa Bulletin issued by the U.S. Department of State shows a "final action date" of May 4, 2008 for applicants in the Family-based F4 visa category (brothers and sisters - who are nationals of most countries - of U.S. citizens). While that may appear to indicate that there is only two additional years of backlog for people in that category with Priority Dates in 2006, in fact it is common for less than a year of backlog to be cleared each year. Priority Dates progress and retrogress, and, regrettably, it may take significantly more than two additional years for your relatives' Priority Dates to become "current." Once they do become current, they should be able to "consular process" in order to enter the U.S. and become Lawful Permanent Residents (to get "Green Cards"). If at that time your income is insufficient to sponsor those family members according to the Poverty Guidelines for the applicable family size, then it will become necessary to have "joint sponsors" for those applications. Generally, a joint sponsor may be any U.S. citizen or Permanent Resident who has sufficient documentable income and who is willing to assume the responsibilities contemplated in the Affidavit of Support document. It would be wise for you and your family members to consult with an immigration attorney.