nebulous

Sup.

baby advisors are cute

Indead.
Wander if their alien assassins, that got their limbs cut off and did some magical ritual and turn them into fat slugs, and gave them a testicle like tongue.

I honestly doubt it. If you ask me, alien assassins are probably, like cremators, highly modified humans who have been captured and slightly or heavily mechanized

and I'd assume that the advisors are the leaders of the combine, unless valve make HL3 and pull a falling skies where (SPOILER ALERT) the ones who are thought to be leading everything are just puppets like everything else seen up untill you really got their attention

http://vignette1.wikia.nocookie.net/half-life/images/7/71/Alien_Assassin_-_walk.jpg/revision/latest?cb=20090603171315&path-prefix=en
Maybe aliens, the head doesn't look human.