Tenant with service dogs

[Marion Lee]

We have someone that is interested in renting one of properties in Virginia that has 2 service dogs. She says she can produce documentation stating that her children need the service dogs. We're fine with the 2 service dogs but the prospective tenant has stated that the family is eligible for 2 more service dogs, 4 dogs total. Can we place a limit on the number of service dogs in the lease? 

I've read the landlord tenant laws and didn't find anything on service animals. 

Thanks in advance for your help

Marion