Joint retainers are not permitted for family law matters. A joint retainer would pose a direct conflict of interest and is therefore not practicable. You and your ex-partner will each be required to retain your own lawyer.
Each lawyer is required to explain every step of the process and provide advice to their clients. If the parties want to mediate the issues, then they can jointly hired a mediator to help them resolve the issues. These issues will later be put into a Separation Agreement and each party will have to hire their own lawyers to provide them with Independent Legal Advice.