Most likely, though ultimately up to the DM
It seems based on similar questions that yes you could use the Rogue Assassin's Impostor Feature to impersonate another person via Awakened Mind. There does not seem to be any official rules specifically stating how you sound when using Awakened mind, however there is an unofficial ruling from Jeremy Crawford stated in this answer to a similar question:
You sound like yourself when speaking via telepathy, although as DM, I
allow attempts at telepathic deception.
Your DM may decide that a Deception Check is in order to see if the creature you are talking telepathically with can see through your ruse. With Impostor, you would have advantage on this deception check:
Your ruse is indiscernible to the casual observer. If a wary creature
suspects something is amiss, you have advantage on any Charisma
(Deception) check you make to avoid detection.
Trying to convince a creature that they could read the thoughts of other creatures may be harder, as you are trying to impersonate multiple creatures. I would allow this with a few Deception Checks here and there to convince them, the DC for which could change depending on the success of previous rolls. If you had taken the time to use Impostor on every creature nearby when you attempted this, you would once again have advantage on the Deception checks.