Updated: Feb 3
This is totally forbidden. On one hand, two distinct tenants cannot physically share the same rental property and the landlord cannot receive two rental incomes from the same property for the same period.
Be sure that your rental contract stipulates that the property is free at the time of entering and that the previous rental contract has been terminated.
When a tenant wishes to extend the duration of the rental period, this can only be done if a new rental contract covering the same period as that of the extension, has not been signed yet.