Can one sell the whole of the property on a 50-50 share without the other consent?

Answer 1

No. The first rule of conveyancing is that a grantor can only sell what they own. When there are multiple owners of property any one owner can only sell their proportionate interest in the property. Therefore, if there are two people who own a single property, one can only sell their one-half interest. It may be difficult to find a buyer if the property is a single family dwelling. The one half interest may be conveyed if the property is held as tenants in common or as joint tenants.

The situation becomes more complicated if the property is owned in a tenancy by the entirety, a special tenancy reserved for married people. In a T/E the "survivorship rights" of the other cannot be severed. In some states one tenant by the entirety cannot sell their interest in the property. In some states they can transfer their interest but the grantee acquires a tenuous title that depends on the life of the grantor.

For example, Norah and Ethan owned property as T/E in Massachusetts. Ethan decided to leave (there was no divorce) and transferred his interest in the property by deed to his brother Liam. In some states that deed would be void. In this case the title would play out as follows. If Norah died then Liam would become the sole owner of the property. If Ethan died then Norah would become the sole owner because her survivorship rights with Ethan could not be severed. Liam would be out of luck.