This is a difficult question, perhaps without a good practical answer. If they want to fight the possible eviction, they should get an attorney to represent them and force the landlord to prove in an eviction proceeding that they violated the lease terms EVEN ONCE, and to bring witnesses and/or affidavits of the neighbors, and point to the terms of the lease which they said were violated.
Keep sending rent checks, and if they are returned, have them endorsed over to the attorney's escrow (trust account) for the benefit of the landlord. I assume this is private, not public housing, which has stricter rules over tenant behavior.
Faced with an actual eviction proceeding where the landlord has to PROVE this stuff, and the other complaining tenants might not like to be involved (complainants like this who are more busybodies than people who are actually annoyed, like noise or party complaints tend to not want to out themselves and are more passive/aggressive), and the costs and hassle of an eviction proceeding, the landlord might rethink his opposition.
And I think you'd have a 50:50 chance of having a sympathetic judge, most are tenant-oriented, unless the landlord can prove real damages or non-payment of rent.
By the way, you are Californians in Santa Rosa: was the marijunana user a state-legal user of medical marijuana with an current recommendation and id card? Although public use or use in this situation is probably never a good idea, the fact that the behavior wasn't as outright illegal as it is in many states would be relevant and pose an additional hurdle for the landlord.
Personally, I'd be inclined to fight the landlord, just to fight fire with fire. I think you have a pretty good chance of winning and the aggravation and entertainment factor to the landlord would be enjoyable. The worse that can happen is eviction anyway, and the tenants are certainly going to be looking for a new place at the end of the lease term. I wouldn't expect to get the security deposit back and the last month's rent is presumably paid in advance.
This answer is provided under the Avvo.com “Terms and Conditions of Use” (“ToU”), particularly ¶9 which states that any information provided is not intended as legal advice or to create an attorney-client relationship between you and me or any other attorney. Such information is intended for general informational purposes only and should be used only as a starting point for addressing your legal issues. In particular, my answers and those of others are not a substitute for an in-person or telephone consultation with an attorney licensed to practice in your jurisdiction about your specific legal issue, and you should not rely solely upon Legal Information you obtain from this website or other resources which may be linked to an answer for informational purposes. You understand that questions and answers or other postings to the Site are not confidential and are not subject to attorney-client privilege. The full Avvo ToU are set forth at http://www.avvo.com/support/terms . In addition, while similar legal principles often apply in many states, I am only licensed to practice in the State of New York and Federal Courts. Any general information I provide about non-New York laws should be checked with an attorney licensed to practice in your State. Lastly, New York State Court rules (22 NYCRR Part 1200, Rule 7.1) also require me to inform you that my answers and attorney profile posted on the Avvo.com site may be considered "attorney advertising" and that "prior results do not guarantee a similar outcome".
How this is handled will depend both on the lease agreement and CA tenant/landlord law. You should certainly consider retaining an attorney to prevent being evicted. You should also inform yourself by reviewing the lease terms. Check the lease for the following:
1. What does the lease says about nuisance? Does it include or define that word ? And if so, does that term seem to include/cover the "problem" activities, or not? If the marijuana smoking/use was illegal it may well consititute a nuisance (that term is usually defined to include illegal activity). However, there is a question of whether the nuisance remains actionable once the activity has been abated (ceased).
2. Also, check the lease to see what it takes under the lease terms to get evicted. What does it say has to happen for the landlord to evict? Check any sections headed "default." In some cases there is an opportunity to "cure," or fix aproblem before you get evicted.
I agree with the posts from counsel and will also add that you should check for any addendum to the lease re marijuana use as these are very common in Northern California, if use of same is strictly prohibited and if the Landlord can establish that, it is possible that the violation is not a curable breach under CCP 1161(4). Generally it will require evidence that this was not a single incident. Good luck.
These answers are not intended nor shall it be deemed to be the rendering of legal advise, they are given based on the information provided which is insufficient to give meaningful advise. These answers shall not be construed as part of the creation of an attorney-client relationship, nor shall it impose an obligation on the part of the attorney to respond to further inquiry. The Questioner has responsibility of obtaining legal advise from an attorney and is urged to do so.