Short answer. Not against each other. Rule 130, Section 24 lists joint clients as an exception: a communication on a matter of common interest, made to a lawyer retained or consulted in common, is not privileged when offered in an action between any of the clients, unless they expressly agreed otherwise.
What the law says
if the communication was made by any of them to a lawyer retained or consulted in common, when offered in an action between any of the clients, unless they have expressly agreed otherwise
Rule 130, Section 24 — Disqualification by reason of privileged communication[s]. Read the full provision →
The privilege still works against outsiders
The exception is narrow and its narrowness is the point. Where two people consult one lawyer together, what they said remains privileged as against the rest of the world — a third party suing one of them cannot reach those communications. What the exception removes is the privilege between the joint clients themselves, and only when the communication is offered in an action between any of the clients. Outside that setting, the ordinary lawyer-client privilege continues to apply.
Why joint clients cannot hide behind it
Both clients were in the room. Both heard what was said, and both received the same advice on the same matter of common interest. A privilege is a rule about confidences, and there is no confidence between two people who were told the same thing at the same time by the same lawyer. If they later fall out, allowing one of them to seal off that shared conversation would let a person suppress evidence the other already possesses — and would make the shared consultation a trap rather than an economy.
"A matter of common interest"
The exception applies to a communication relevant to a matter of common interest between two or more clients where the lawyer was retained or consulted in common. Both elements have to be present. Two people who each separately engaged the same lawyer on their own distinct matters are not joint clients merely because the lawyer is the same; the arrangement has to be a common one on a shared subject. Where that is unclear, it is worth settling in writing at the outset.
The parties can agree otherwise
The clause ends with unless they have expressly agreed otherwise, which gives joint clients a way to change the default. An express agreement — made when the joint engagement begins, not after a dispute has arisen — can preserve confidentiality between them. Business partners, co-owners and family members entering a shared engagement are the people most likely to need it, because they are also the most likely to end up in an action against each other later.