Currently rental agreement allows only 2 adults, now it is 4 adults?
If the lease is month to month, why bother with an eviction process? Give them however many days notice you must legally give them, then tell them that you will not be renewing their lease. Then if they dont leave you can take firmer action. Let me ask you this, though. Yes, they are in violation of the terms of their lease, but otherwise are they causing a problem? Are they too noisy, making messes, taking up more than their share of parking, that kind of thing? It might make more sense to get the other adults on the lease. If you boot them, then you will have an empty unit that you have to clean up and then rent out. You might also talk to the tenants to see if (a) they understand that they are violating their lease and (b) how long they expect the situation to last. I imagine that they are probably helping out family or friends in need. Of course that does not mean their familys problem should be yours, but it is worth seeing what the actual situation is.