I'm not a lwayer, but I've watched a lot of "Law & Order" ...
RICO is a crime with underlying predicate acts. For Biden, Inc., the underlying predicate acts would probably include conspiracy, money laundering, tax evasion, and influence peddling.
It might be easier to prove that Hunter was the kingpin than Joe. Hunter got money, ho's, and crack.
I think it's more difficult to prove that Joe was the kingpin, because it has yet to be proven that Joe benefitted more than Hunter. But, Joe could be looped in as a conspirator, participant, or contributor of Hunter's criminal enterprise by Joe making conspicuous phone calls to Hunter while Hunter had clients or potential clients in the room.
Legally, it's easier to make the case the Hunter was the head of the criminal enterprise with Joe as a participant, conspirator, or contributor.
RICO is not a criminal act; it is a collection of underlying of predicate acts that demonstrate the existence of a corrupt criminal enterprise.