Legal Question in Family Law in Washington

I would say no. The only plausible way to do so is if the attorney first wrote to the other spouse and asked for their permission to represent the other spouse in a legal separation. The lawyer would need to indicate in writing that before agreeing to waive their right to not allow this lawyer to represent the other spouse, they ought to consult independent legal counsel.

Even if all that happens, if I were advising that lawyer, I would say be careful and consider just referring both parties out to other lawyers to avoid any possible conflicts of interest. To the clients, I would say that if your former attorney now represents someone on the opposite side of a case, if that at all makes you uncomfortable, you ought to write the lawyer and say why you are uncomfortable (namely because you are my former attorney) and ask that they withdraw, given that you believe they have an ethical conflict of interest.