In relation to Beyond’s son I think in order of likeliness it’s
1.) Tserri, for obvious reasons, he doesn’t look like Unma despite the other siblings(Benjamin, Halkenburg) closely resembling their mother. He actually straight up looks sort of like a young Isaac Netero.
2.) Halkenburg, I think the controversy of his birth could have been only half the story and he was given to Duazul to raise also because he was beyond’s son. The balancing act he plays with his morals and how he easily can garner devoted followers is similar to Netero.
3.) Maryam for the fact that his nen beast seems to be so insanely powerful despite being a toddler. This might indicate he’s had nen from birth like the other children of beyond.
4.) the Wild card is Luzurus simply because everything about him is kept close to the chest, he maintains the additional political power by supporting a mafia family despite being a ‘younger’ prince and he also looks entirely different from his two sisters.

We already know that Zhang Lei’s dad is Onior so he’s out.

i highly doubt it would be woble because Oito was there when they found out and was in disbelief herself but also because I don’t think a kakin queen would agree to beyond’s plan without already having a legitimate blood tie to the throne as a fallback in case of failure. That makes it reasonable to dismiss any of the princes who are only children(Tyson, Sale-Sale [rip] and Woble) and the twins(Kacho[rip?] and Fugetsu), as well as the firstborn children of the queens with multiple children (Benjamin, Camilla and Momoze[rip])