The reason for the arrests seems to be that Hamas tilted towards Iran in accepting funding and the Saudis look at any allies of Iran as implacable enemies.
Last September, after trying to negotiate behind the scenes, Hamas came out with a public statement against the Saudis for the arrests. Now Hamas is publicly protesting, saying that the arrests are political (which seems likely) and their only crimes is supporting jihad (which is also likely.)
On Sunday, the trial of the al-Khaduris began, and it appears that they will return to court the beginning of May.
Of course, Hamas supporters are claiming some sort of Israeli conspiracy behind this.
This infighting is not being widely reported in the West.