Which of the following is a form of multiple ownership in which each owner possesses an undivided proportional interest in the entire property, although the ownership shares need not be equal

Tenancy by the entirety is a special form of joint ownership that can only occur between married couples, where each spouse has an equal and undivided interest in the property. This type of ownership includes the right of survivorship, meaning that if one spouse dies, their interest automatically passes to the other. Thus, it does not allow for unequal shares among multiple owners.

Tenancy at will is not a form of ownership but rather an arrangement where a tenant occupies property with the permission of the landlord without a fixed lease term. This type of tenancy can be terminated at any time by either party and does not involve shared ownership interests in the property.

Joint tenancy involves multiple owners holding equal shares of the property with the right of survivorship. If one owner dies, their share automatically passes to the surviving owners, resulting in equal ownership interests. Therefore, it does not accommodate unequal shares among owners, which is a key feature of tenancy in common.