if her theory of Beyond having a kid in the princes is true I think the guy with the afro hair would make the most sense as he's not too obvious like Benjamin or Tserridnich, but not as much of a longshot as the peace prince. (and we know it's not Arrow/important prince - I've forgotten all their names - unless Beyond is intentionally not informing the prince if their lineage)
Could also be Wobble as a twist, but I think that's too obvious of a twist for Togashi to pull it.
For the others Fugetsu seems impossible as she has a sister and will probably (sadly) die, and Zhang Li (idk, coin guy) just seems kinda irrelevant since he gets screentime and doesn't do much with it (unlike afro who just doesn't get it), science prince is possible, but making the alliance with her seems to mean she knows its not her for some reason. Could be Camilla, but I think she's too crazy for Beyond to be putting stock in her, and I'd like her ability to be in use of a third party more than his side.
Tbh though there's not really any I'd hate for it to be (but do hope its not Benjamin, Tserridnich, or Camilla, id rather it was more twisty plot than that)