User blog comment:Fintin/Poneglyph of Dressrosa/@comment-24799733-20140509224831/@comment-24799733-20140510205622

What the anon said is true but the Nefertaris were the only of the 20 that stayed behind.. this tells me they're most likely good in some terms, fact that's backed up by the fact that Oda protagonized their family during an entire arc... I doubt he would've done that with any other family i. e. Donquixote.

I think one of the main reasons for the Nefertaris to stay behind was to protect that Poneglyph... but it's just a guess, who'd know?