According to sections 3.4-5 through 3.4-9 of the Code, a lawyer may jointly represent multiple clients provided they comply with all the required elements.
3.4-5 Before a lawyer acts in a matter or transaction for more than one client, the lawyer must advise each of the clients that:
(a) the lawyer has been asked to act for both or all of them;
(b) no information received in connection with the matter from one client can be treated as confidential so far as any of the others are concerned; and
(c) if a conflict develops that cannot be resolved, the lawyer cannot continue to act for both or all of them and may have to withdraw completely.
3.4-6 If a lawyer has a continuing relationship with a client for whom the lawyer acts regularly, before the lawyer accepts joint employment for that client and another client in a matter or transaction, the lawyer must advise the other client of the continuing relationship and recommend that the client obtain independent legal advice about the joint retainer.
3.4-7 When a lawyer has advised the clients as provided under Rules 3.4-5 and 3.4-6 and the parties are content that the lawyer act, the lawyer must obtain their consent.
If you are jointly representing clients and a conflict arises between them, the Code further provides:
3.4-8 Except as provided by Rule 3.4-9, if a contentious issue arises between clients who have consented to a joint retainer,
(a) the lawyer must not advise them on the contentious issue and must:
i. refer the clients to other lawyers; or
ii. advise the clients of their option to settle the contentious issue by direct negotiation in which the lawyer does not participate, provided:
A. no legal advice is required; and
B. the clients are sophisticated.
(b) if the contentious issue is not resolved, the lawyer must withdraw from the joint representation.
3.4-9 Subject to this rule, if clients consent to a joint retainer and also agree that if a contentious issue arises the lawyer may continue to advise one of them, the lawyer may advise that client about the contentious matter and must refer the other or others to another lawyer.
After the conflict has been resolved, it is possible to resume joint representation if you receive the informed consent of all the clients. For more information on when joint retainers are appropriate and when they are not, please see the Commentary to section 3.4-5 in the Code.
When considering joint representation, it is vitally important to be aware of Commentary  to section 3.4-7. It states as follows:
 Consent in writing, or a record of the consent in a separate written communication to each client is required. Even if all the parties concerned consent, a lawyer should avoid acting for more than one client when it is likely that a contentious issue will arise between them or their interests, rights or obligations will diverge as the matter progresses.
When advising on and obtaining consent to joint representation you may wish to consider section 3.4-9 and determine in advance whether it would be appropriate for you to continue to represent one party if a contentious issue arises and, if so, which party that will be. Determining this in advance while all parties are on good terms is much easier than trying to negotiate consent after contentious issues have arisen. For example, if you act for a corporation and for shareholders in setting out the terms of a shareholder agreement, it may be wise to have advance consent to your continuing to act for the corporation and/or certain shareholders in the event of a dispute between shareholders.
Should you decide to represent two or more clients, here is a sample joint retainer agreement provided by the Law Society of British Columbia for your reference.
Note that improperly informed joint retainer/joint representation situations are both a regular cause for complaint to the Law Society and a common subject of inquiry from lawyers seeking advice. It is particularly important for clients to understand that information will not/cannot be kept confidential from the other member(s) of the joint retainer, and even a request of the lawyer to do so may result in a requirement that the lawyer withdraw from representation of both clients. Note that the client information aspects of a joint retainer situation listed in s. 3.4-5 are mandatory and should therefore be documented. If you cannot provide evidence that you warned the clients in this regard, you will be presumed not to have done so.