Re: Two living trusts hold deed to real property.
This is a good question. I think the analysis starts with how you hold title to the equally-owned real property now; you also don't say whether you are registered domestic partners under the new California law. Registered domestic partners' property is often subject to different rules (e.g., some of it may be community property).
Civil Code section 683, defining joint tenancy, certainly seems to make it possible for two trustees of two separate trusts to hold title as joint tenants. I believe that in transferring the property to the trusts particular care in drafting would be necessary to assure that the requirement of a simultaneous transfer of equal interests was met.
On the other hand, I see no particular reason for creating or maintaining joint tenancy once the trusts are set up....properly-drafted trusts can handle your desires and expectations as effectively or even more so than reliance on joint tenancy.
Note that there is also the concept of a "joint trust," in which both partners place their property in a single trust, which can have one or more trustees. Although sometimes used, most lawyers feel the problems outweigh the benefits, and separate trusts (as you seem to envision) are more common. The problems include the tax issues you allude to (whether a taxable gift occurs, etc.).
My advice would be to have two trusts drawn up by an attorney or attorneys, then fund them with whatever interests you currently hold in the real property through separate grant deeds, and to have a local title company prepare and record the deeds using whatever form of deed they customarily use, and inserting whatever granting clause they recommend under the circumstances.
A plain-vanilla set of transactions is least likely to bring about tax problems or later difficulties in administration by successor trustees upon a trustor's death.
Upon funding your trusts, be sure to notify your lender, insurer and tenants, if any.
