Anyone in "a bit of a mess separating ownership" and in which one of the other parties has already retained counsel shouldl seriously consider retaining their own attorney.
This is already a contested matter in which the parties have different interests. The idea that communications with opposing counsel will not "come back to bite anyone should negotiations break down and we end up in court" is almost certainly unrealistic.
The NC and Raleigh bar associations can assist you with referrals.
The foregoing is for general information purposes and does not establish an attorney-client relationship.
You need a lawyer. Your question is so shockingly naive and wrongheaded that it is hard to know where to start.
The lawyer for the opposing party is absolutely going to use the things that you say against you both in the negotiation and in court. That is his/her job. Even without revealing anything that should not be revealed, the lawyer is going to use the information that you share to hurt you. You are setting yourself up to get eaten alive.
This is no place for amateurs. Hire a lawyer.
The Confidentiality Agreement you seek us to comment about would be giving you free legal advise, and also be the unauthorized practice of law for any attorney not admitted to practice in NC.
As a general principle, it appears to be acceptable, but none of us can comment upon how informattion discussed may be utilized should a settlement not be reached, whether you will disclose information that will lessen your outcome or increase one of your partner's outcomes.
I would hope a court would not allow information revealed during negotiations to be used in court, but it is like telling a jury to disregard a remarked stated by an attorney or witness. One the statement has been made-such as "When did you stop hitting your wife."- the jurors' minds have been poisoned. The opposing counsel now knows something he may not have known before and can secure this information through discovery.
HIRE AN ATTORNEY!! The old addage goes: He who represents himself has a fool for a client.
The foregoing is not intended to be legal advice upon which you may rely as I have not been retained for this purpose.