At least speaking of this forum, I don't think that they get passes. Fredo, in particular, is seen much more darkly here than seems to be presented in the movie.

Why some seem to get a pass in the movie itself is more of a "how." One technique is just using emotion, like Fredo in the boathouse, to create sympathy. Another is to show something completed, as with the prostitute's murder, so that Tom and Fredo aren't actually shown participating. The audience can only process so much in real time.