if I prohibit pets by lease for 1 tenant do I need to do for all?

[Marsha Burks]

The lease stipulates 'No pets". However, a very good tenant of 4 years recently asked if she could have a small dog due to feeling lonely from quarantining. I'm ok with granting this. However, I also rent the adjacent attached townhome to a couple for the last 5 months. They pay rent reliably but aren't the best housekeepers, nor ground keepers.  I'm concerned they would ask for the same. 

Am I legally responsible for having the same lease terms for pets for ALL 4 properties in the same community ? These are walkup townhomes. Six townhomes per building. I own and rent out 3 adjacent units.