Yes, they are all different lengths, corresponding with the number of seats. The 145 is 98 feet long, the 140 is 93 feet and the 135 is 86 feet.
I'm guessing that you are asking because, in contrast, Bombardier opted instead to certify multiple configurations for a single cabin size in its regional jet line (e.g., the CRJ-440 is basically a -200 but with a maximum of 44 seats instead of 50, and the CRJ-705 is a -900 with only 70 seats).
These are simply two different approaches to the same problem, i.e., airlines only want to pay for the capacity they need (or, in many cases, the capacity to which they are limited by scope clauses). Embraer's solution means additional manufacturing costs, whereas Bombardier's solution simplifies manufacturing but suffers from the inefficiencies of hauling around more airplane than is strictly necessary.
Common sense is not so common. -Voltaire