If you have a lease the other party should not be able to change the agreement by themselves. But take your lease to a lawyer or the Montana Legal Services Association for a review. You and the other tenants may have a basis for a court claim. Act as soon as possible.
DISCLAIMER: The forgoing comment is for general educational purposes only, and is not legal advice upon which the reader may rely as the commenter has no actual knowledge of the facts of the case, has not interviewed persons or examined evidence, and has not researched the applicable law. The comment is based only on the facts provided, which are extremely limited, and may or may not be true. Complete defenses may prevent the success of any claim. Competent legal advice should always be obtained before taking any legal action or filing suit. Readers employ any information provided herein at their own risk.
If your lease is written, then the terms of the written agreement controls. Generally speaking, the landlord cannot raise rent without certain notice given. And the landlord cannot change your lease to a month-to-month where the term has not expired.
Regarding the other claims you make, that is matter of whether the landlord has breached his duties under contract or law. MT Statutes impose upon landlords certain duties. You should consult with an attorney to see if the landlord has violated MT law and/or your contract terms.
This is not meant to be legal advice but only a general response to a general question. Legal advice requires more attention to details and circumstances to be accurate and reliable. Do not rely on this response as legal advice. If you want legal advice about your matter, you must set up a consultation with this attorney by calling (406)756-911.