Saudi politics and personal relationships are a mess. It is true that Bin Laden is a member of a very powerful family in Saudi and so obviously has a lot of personal connections there as do his close associates. He is however estranged from that family and has been for a very long time, but may have some in Saudi who have grievances against the house of Saud and are sympathetic to the jihadis.

Al Qaeda and many other jihadi outfits procure a lot of their funding from Islamic charities and schools (Madrassas) with complex and very opaque financial dealings. Also the Saudi government and individual Saudis donate to many Islamic charities, so its highly likely some of that money ends up with the jihadi's including Al Qaeda.

So yes there's almost certainly some truth to the allegations. Some powerful Saudis may secretly support them, some donate to charities and the money ends up with them, but no this is not official Saudi state sponsorship of Al Qaeda. In fact Al Qaeda consider the Saudi royal family and all of their associates to be apostates (essentially heretics) who can be killed summarily and they advocate for regime change and the establishment of a Caliphate.

Like I said, it's a real mess of family loyalties, rivalries, swinging political fortunes and opaque dealings. Game of Thrones has nothing on these people. Just look at what happened to Jamal Khashoggi.