Oooh! Savunn and Bob just got a taste of their own medicine, She may have done a good job figuring out who Brooder is, but she's still not on his level, and he just reminded them both of that. :)
It may be simply be that the way Bob communicates is similar to the bone phone that Savaun was given, and that allows Brooder to hear him as well..in reverse. ór it could simply be that Savaun is unconsciously Subvocalizing when bob is talking. Although that requires a very sensitive microphone, and may be the real reason he asked Lynda to leave.
Of course Adam could just be self socially isolated because he fears what would happen to any one he loves by the big baddies still out there looking for leverage.