What's happen if one of the tenant didn't sign the lease but continue to stay?

[Susanna Oeidy]

I do need an experts to guide me. My tenant sign a 5 months lease - 4 travel nurses. One month prior to the expiration, Three of the nurses sign the renew the lease with a new term and price for extra 2 months. Everyone sign the first extension.

They request another extension again till the end of Dec 2023. I do second extension with new term and price with addition of a new member in the contract. 3 out of 4 sign the lease. Only one left never sign the lease.

Those 3 is agree to stay till Dec 2023.

One request special check out time by Oct 31. granted by landlord on the same second extension but never sign back.

What's the legal way to take care this situation? Because the one that do not sign the lease keep changing move out time with text messages. Can text messages consider official?

I believe since she never sign doesn't meant she can get away with it. It's become month to month and she needs to give a proper 30 days notice. Otherwise, her security deposit can be claimed by the landlord?

Please advise. Thank you for your help.