I would think that if the GAL was with him, they may have had to allow some bit of visitation.
However, IMO, FD showed up without the GAL and expected to Take the children.
With JD missing, he more than likely Assumed, that he would get automatic immediate custody of the children.
I Absolutely believe he planned to immediately abscond to Greece with the children, MT, and MT's daughter.
He and his attorney met with LE around Noon on that Saturday and it was reported that he arrived in Manhattan in the late afternoon.