Begum's case is different, her nationality seems to be in doubt technically, IMO an international court should adjudicate on this.
I don't think Begum's nationality really is in doubt, much though Priti Vacant would like it to be. Like T.May with Hamza, she'll end up losing case after case about it but keep finding another way to stop her coming back into the country until someone else has the job.
Begum is, sadly, a British citizen and problem no matter where her parents were born. And quite a problem it is. She was a child when she left to join ISIS. But still above the age of criminal responsibility. But did she really know what she was doing? Had she been groomed? We don't blame the 15 year old girls who were groomed for sex by the Rochdale gang, so why blame her for her stupidity in joining ISIS? But now she's an adult and since being an adult has potentially committed crimes. Where should she be tried for that? Was it a consequence of earlier immature actions anyway?
The Rochdale groomers have been tried and convicted as adults for their heinous actions so no matter what technicality they are claiming to try to stay in the country, they should be deported if they are not British - even on a technicality.