The detention by the SDF in Syria of two former British citizens, who became ISIS executioners and were nicknamed 'The Beatles', has once again returned to political in-trays what shall we do?

A BBC report:

Raffaello Pantucci, RUSI, argues that:
So the answer for cases like those of the two captured Beatles is a fairly obvious one. They should suffer the legal consequences of their actions in whichever jurisdiction is appropriate. If they can be linked to criminal activity which the United States Department of Justice can and wants to prosecute, then they should be sent to America and prosecuted to the full extent of the law. For the range of others who have gone to fight from the United Kingdom, each one needs to be dealt with in on a case by case basis. This may produce a long list of headaches for the Crown Prosecution Service, but this is the appropriate response from our country with its proud open and free judicial system.

I cannot see anyone, even Japan, racing to have them delivered into custody for a trial. The USA has Guantanamo Bay and prefers not to have criminal trials, although in theory that door has not been closed for those few who remain there. Now they are no longer UK citizens I cannot see the UK will have them here, although IMHO it would be a good thing - justice is what we say they deserve, so do it. A big assumption the evidence various parties hold is available.

Not sure about the legalities of having them handed over by the SDF.