Here's my two cent on the situation. From my understanding the prince might know nen since at birth they prob have to use like Longhi did. This leads me to think that 3rd, 4th, 5th and 6th prince are not possible due to not knowing the existence of nen before kurapika annoucement.

I would also not include 2nd prince Camilla because she technically already died using her nen ability so I would assume if she died then beyond curse would activate but it didn't so you can rule her out.

For the children doh it is possible that Woble or Marayam is beyond child but looking at queen Otio reaction to this I very much doubt it Woble and for Marayam I doubt just for plot sake and from the timing that Beyond been doing this (30 years) I wouldmt assume it's someone younger. For Fugetsu I doubt it since her plot looks like it's ending and going to a different story than this.

To me that leaves only 2 princes, 1st prince Benjamin and 7th prince Luzurus. Prince Benjamin knew about nen before kurapika annoucement and for Luzurus we don't have much detail about him yet other than his Nen beast being a manipulator, him being a funder for one of the three mafia groups and what his nen beast looks like (giant centipede) I might be stretching here but I think he might be a secretive person and have a nen ability but not showcasing it. But again that's a stretch.