On the subject of al-Qaeda,
I watched that whole 10-minute clip, and not once did they say that terrorists don't exist, or that bin Laden didn't do 9/11. All that they said was that al-Qaeda as a well-organized, coherent group does not exist, and with surge of patriotism and nationalism that followed 9/11, that isn't hard to believe.
However, it doesn't disprove that a wealthy Saudi man who hated America didn't get a few other people who hated America together to carry out the worst terrorist attack on America in our nation's history. I never heard anything of the sort.
On the dancing Israelis,
All of the reports seem to stem from the observations of a New Jersey housewife named "Maria." I have not seen any credible reports of multiple witnesses calling in. Even though the men may have been Israeli spies, there is no evidence that they had foreknowledge of 9/11, since she first saw them while watching the WTC. An FBI investigation turned up no evidence that the men knew about 9/11, only that they saw the event happening and decided to film it.
And the original report of explosives found in a van on a New Jersey turnpike (not in the dancing israelis' van) was corrected 8 minutes later.