Why didn't they go after Cynthia's husband?

I always found that weird too. Perhaps it's because they felt that, at that point, they couldn't do anything about it. Cynthia had already taken her life, and their whole plan (at first), was to get even with their exes. Mostly through monetary gain. It's not until much later that Annie narrates that eventually they decided to turn the abandoned buillding they bought into a crisis center for women. They were all feeling some amount of guilt for not being there for Cynthia when she needed it most, so to fix that and make sure it never happens again, they open a crisis center to help women in that position.

Because they had no in with him. The women were still involved with their exes. But Cynthia killed herself and removed any direct line to him. And also, in the end they decided to honor her memory instead.

In the book they do. They go after his business and bankrupt him and also use cynthias brother to spy on the second wife and find out stuff that causes the two to separate.