Hi Laura -- I'm Scott!
First, I have to say that lawyers in this forum cannot provide specific legal advice to specific legal matters, because no lawyer client relation exists. We can only talk about the law generally.
But hopefully I can help by providing some perspective on landlord-tenant relations in similar circumstances as described.
Tenants need not pay rent to be considered tenants with respect to the law.
And tenancies need not be in writing unless there is a specified term for a year or longer.
Tenants who have no written or oral lease agreement with a landlord fall into one of two categories:
tenant at will = this is a tenent who remained in possession after the original lease term expired, but with the consent of the landlord and generally under the terms of the original agreement except for the time term, and the tenant continues to pay the periodic rent -- weekly, monthly, annally, or whatever).
This is usually what happens at apartments after the lease expires, where most standard lease indicate that after the original term the tenancy is "month-to-month" unless a new lease is formed.
This "tenancy at will" can be terminated at will by either party for any reason or no reason at all, with due notice as described in the original agreement (in a monthly payment situation, notice would be 30 days; in a gratuitous situation it would be "reasonable notice").
tenant at suffrance = is a tenant in possession of a premises entirely at forbearance of -- or at the sufferance of -- the landlord. The tenancy can be terminated by either party at any time for any reason or no reason at all, and with notice or without notice. In a gratuitous tenancy situation, no notice whatsoever is legally required.
Because both these tenancies require the landlord's permission, there is no chance the tenant can seek legal title to the premises under the theory of adverse possession.
A legal agreement may shade existing relations, even if merely describes what currently exists; and if it adds conditions for each party, then it may color the relationship even more.
If parties are content in their informal, personal relations, the question is whether either feels the need for what "protection" formalization brings weighed against any shadows that might be cast over the relationship.
In a gratuitous tenancy at sufferance, even a notice agreement might be more obligation than either party wants to commit to.
It comes down to what parties want and are comfortable with.
I hope you found some this helpful in adding perspective: If so, I would greatly appreciate acceptance & a positive rating! thanks! scott