Parel station in Mumbai is at walking distance from Khaitan, Trilegal etc. Do associates/SAs/MAs also travel to office in local trains?

Sure, if you stay on Western line

I doubt if associates/SAs from Trilegal or KCO actually take local trains. Even if they do, must be to avoid the infamous Mumbai traffic.

I haven't seen a single Tri/KCO SA and above, taking local to the office.
Infact even the A0s come by cab.

Dont. You are not allowed.