State law does not trump federal law.

Federal forfeiture/seizure laws would have me looking for that answer pronto, as the feds could easily assume your knowledge and complicity in the illegal activity. Have you looked-up breakdowns of federal plant-count levels insofar as penalties...?

If you confront the tenants about this, perhaps they'll get the idea and at least be more discrete. But if they were to get busted after that point, regardless of your involvement in the bust, likely they would blame you. (would they "get even"?)

Despite the fact that being a "snitch" is deemed uncool, if they are breaking laws that MIGHT get your home seized...tough shit. Let 'em go put someone else's stuff at risk.