They have no chances at cracking the 1 billion mark individually. Combined they possibly could with the combination of Pain / Itachi / Obito, due to the hax of their techniques with Kamui, Totsuka, Preta Path and things of that nature.
They could be higher, if Genjutsu worked without the reliance on the enemy having chakra network. But it's essentially nullified in the OP world.
The "Anti-World Government" is blown out of proportions when it comes to Bounties by the OP fandom. Marines' perception of somebody's power dictates bounties for majority of the part combined with having powerful connections + underlings. Fact is any decent Logia, somebody like pre-TS Smoker would wreck most of the Akatsuki organization by himself, due to no Haki from Akatsuki.
It took luffy being allied with Sabo & RA, said to have 7 powerful captains under him, said to have beaten the likes of Katakuri & Cracker (each of whom can solo the akatasuki if there's no Kamui involved), having the Sun pirates, Germa 66, Firetank pirates working under him to have the bounty of 1.5 bil.
Not sure if people here truly understand the sheer gap in physical prowess that exists between the Naruto-verse and the OP-verse.