Ok, first and most blatant thing I notice here.
Drell Assassins are not freelance. Virtually all Drell in the galaxy live with the Hanar under the compact, and Drell Assassins exist not because of any cultural inclination to be assassins, but because the Hanar train them under the terms of the Compact. Drell Assassins are essentially the hand of the Hanar when it comes to things requiring violence, and they keep them very close at all times until such time as they retire, which is not something they get to choose to do, but something allowed to them by the Hanar when the Hanar deem it necessary. If Silas' parents were killed, the Hanar would take care of him, not cut him loose, as, for all that they may sometimes exploit the Drell, they still have their own obligations to ensure the safety of all Drell.

While it is possible to break away from the Hanar (as evidenced by our very own Drell Adept Kosso) it is still rarely done and not exactly easy.
C-sec is the premiere police force in the galaxy, and despite their being portrayed as not so great, they are actually skilled and have protocols in place that would catch his previous occupation, something that would more likely get him a place ont heir watchlist than a job.

Oh and having been in the Blue Suns means Kasy will either like you or literally try to kill you. She's really a bundle of love like that....