Legal Question in Real Estate Law in Washington

In general, no matter whether both the husband and wife are on title, it is enough that only one of them sign the lease on behalf of the marital community that owns the property. This assumes the property is community property to begin with. (You can have situations where a married couple each have separate real estate from prior to the date of marriage.)

There are some exceptions to it being enough that one signer is sufficient, but I think for your purposes with the facts you've given, that goes beyond the scope of your question. So for now, the general rule that each spouse in a marital community has the right to manage the community's assets applies, as does the rule that each spouse has a fiduciary responsibility to the other to manage community assets in the best interests of the community.