First of all, i doubt there is a Traitor, it's a New Character
Secondly, the Reason those Disappearances started happening Two Months ago is because this Person came to Egghead with CP-5
In other words, this Character is from World Government (But He/She is working Independently, so he was Hiding on their Ship).
Thirdly, this Character can control Seraphim cuz He/She possess same Authority as Vegapunk
It's because They are 7th "Unofficial" Vega.
However, it's not because Vega Split himself into 7 Satellites, but because that Intruder managed to Access Punk Records & make it Connect to it, so it started recognizing Him/Her as a 7th Vega (But without others noticing).
For example, Oda could have made all Vegapunks share their Senses & Experiences, but He refrained from doing that, which is very convenient cuz it allows him to create such Intruder without anyone noticing.
Oda hinted at this Danger, when Vegapunk explained his Punk Records & Dream to make it Accessible by Everyone, then Jinbe warned him by saying that Conflicting Ideologies & Bias of People would create Trouble! And instead of Vegapunk replying with a Solution, he said:
"Science wouldn't Progress if we worried about such things"
Fourthly, this Character isn't really a Villain, they simply are against Everyone for now.
However, that will soon change & this Character will become an Ally as He/She is important for Next Arc
Lastly, for how He/She managed to Connect with Punk Records, it's simply related to their Ability (Could be DF)
And they spent Last Two Months studying Vega's Knowledge