If you are not participating in the conversation then you are not a party to that conversation. Recording those conversations are criminal violations of both NJ and federal law. Moreover, in NJ disclosure of an illegally made recording of a conversation is an additional offense. Illegal recordings are not admissible as evidence. I suggest you stop recording private conversations to which you are not a participant and do not have the explicit consent of the one participants to make the recording.
As to the admissibility of legally obtained recordings, that will depend on the content of the recording and whether the proper foundation can be laid to get it admitted.

