1st - House of Saud
2nd - Walton Family
3rd - Koch Family

This list is based off 2016. Each year it will go up or down and of course anyone with real influence, money, and power would avoid being on this list.
Rothschilds and Bush Families, upon many others.

Reference and link to the list:
http://top101news.com/2015-2016-2017-2018/news/society/richest-families-world/