"Assist someone do" vs. "assist someone to do (or "in/with" doing)"
The correct form, as you point out, is 'to assist someone to do (or "in/with" doing)"'.
Quote 1 is from an ESL source, and could be interpreted as 'here to insist you do' or 'here to help you [to] do'.
Quote 2 is ungrammatical. It should be 'assist you in/with doing'.
I couldn't locate quote 3, but comment is as per quote 2.
(Amended and updated based on comment below)