So in the recent Darth Vader comic that was in conjunction with the War of the Bounty Hunters, Crimson Dawn is reintroduced to the Galaxy by Qi'Ra. Long story short, Vader discovers that a particular Hutt is in-line with Crimson Dawn, and that their actions to attack the Executor makes Vader slaughter the entire Hutt Council, other than Jabba. So by the time Jabba dies, there is little to no structure in the Hutt Crime Family.
I'm hoping we get a more detailed explanation in the show, but I'm assuming that within those five years, all the other Hutts who are related to the original council were trying to reorganize. Now, perhaps the Twins quickly noticed that Bib Fortuna took the throne and promptly ensured that his rule was temporary and that at some point, they would resume their positions as Jabba's heir. But then that was screwed over when Boba killed Bib, which is where we're at now.