How can Saudi help fight ISIS when they are their biggest backers?

[YoungDemCA]

13. The Saudi royal family has approx. 15,000 members

Of which, only 2,000 hold most of the wealth and power.

I think it's not only possible but entirely plausible that some of the House of Saud's members fund terrorism abroad as a way to influence and manipulate events outside official channels. In countries like Saudi Arabia, there's not a clear line between the private interests of government officials and the public interest that they theoretically serve (even though they are not a democracy at all, but a top-down hierarchical monarchy, the rulers of KSA still want to maintain at least some level of legitimacy in their country). And Wahhabism is the entire rationale and ideological justification for the House of Saud's rule, along with controlling Mecca and Medina-which gives them (theoretically, at least) some level of legitimacy.

All of this is to say that Saudi Arabia is extremely difficult to deal with.