My question involves landlord-tenant law in the State of: California

I have a rental with 4 roommates on month to month contracts. Only 3 signed the contract initially in August. The heater broke in November and we did not have money at the time to replace it and they withheld rent. We came to a new agreement with lower rent and they were provided space heaters and they paid rent. New month to month contracts were made and all 4 roommates signed and rent has been paid again. The heater is now working. I served 2 of them with 30 day notices a week ago and they are claiming retaliation. When I reminded them that rent is almost late, they said they won't pay because they are seeking legal advice regarding the 30 day notice. I also found out that they both have breached the lease in a couple ways, but I have yet to notify them. If I serve them with breach of contracts now will that be considered retaliatory? Are they allowed to withhold rent again? Thank you