Question about 2 betrayers

Alright the finale had me wondering this so I need to hear opinions:

Ulf and Hugh’s betrayal in book happens while the Blacks hold Tumbleton. Ormund approaches, Roddy runs out, dragon seeds burn the town and then open the gates to Daeron, Roxton and Co. But in show Ormund and the Greens holds the town, and Ulf betrays the Blacks outside the walls before then turning on EVERYONE. If they still had caltrops or some 2nd tumbleton plot lined up for s4, how do they justify Ulf still being at tumbleton? Roxton is there, after finding ormund burnt by Ulf. Why would he let Ulf come back in, much less have any power?