The investment can be made by any adult in the family who wants to move to America. The most important aspect is not who is making the investment, rather what they are investing in and how much.
The EB-5 investment must be at least $500,000 in a regional center. The money for the investment must come from lawful sources. The sources must be verified through extensive documentation as well.
If you have met the requirements, only then would you need to worry about who is coming over with you and obtaining green cards.
Your children under the age of 21 and spouse are both able to obtain green cards. In addition, if you adopted a child, the adoption must have gone through before you immigrate to the United States. For step-children, they have to have been your step-children two years prior to putting in the EB5 application. If you want to bring your parents, you need to become a US citizen first. In case of brothers and sisters, that will take much longer. You will need to become a US citizen and then it will take upwards of 10 years to immigrate them to the United States, even through the EB5 program.