@eutaB4: you have said it right. It also depends on the financial ability that determines the number of family members you can sponsor at a time. Technically you can sponsor as many family members as you wish (spouse, parents, siblings), however, you have to show affidavit of support/financial proof that you would be able to support them once they are here by showing your annual income or total household income, bank balance, real estate if you have, other assets including stock investments etc (or they can show their properties/bank balance in back home as proof that they can support themselves). 

In the form affidavit of support, there is a poverty guideline that determines how much minimum you should earn at least to support to how many number of people. This is a very simple and easy to follow guideline and determines the number of people you can sponsor based on your annual income, bank balance and other assets. 

Hope this helps! Good Luck!