You need a tenancy in common with first right of refusal upon death or sale of one of the tenants. You can pre-determine the amount of the right or you can agree that it be based upon market value at the time one of the tenants die or decide to sell his/her portion.
Keep in mind that under RCW 64.28.010
Joint tenancies with right of survivorship authorized -- Methods of creation -- Creditors' rights saved.
Whereas joint tenancy with right of survivorship permits property to pass to the survivor without the cost or delay of probate proceedings, there shall be a form of co-ownership of property, real and personal, known as joint tenancy. A joint tenancy shall have the incidents of survivorship and severability as at common law, including the unilateral right of each tenant to sever the joint tenancy. Joint tenancy shall be created only by written instrument, which instrument shall expressly declare the interest created to be a joint tenancy. It may be created by a single agreement, transfer, deed, will, or other instrument of conveyance, or by agreement, transfer, deed or other instrument from a sole owner to himself and others, or from tenants in common or joint tenants to themselves or some of them, or to themselves or any of them and others, or from husband and wife, when holding title as community property, or otherwise, to themselves or to themselves and others, or to one of them and to another or others, or when granted or devised to executors or trustees as joint tenants: PROVIDED, That such transfer shall not derogate from the rights of creditors