It all depends on your contract wth them (assuming there is a formal contract). If the contract says pets are not allowed, then they are in breach by keeping them, and you can tell them they either get rid of the dogs or leave the property themselves. If they had agreement i the contract or written agreement subseqent to the contract tht they could have pets, then its harder.
In that circumstance, you need to check the contract for anything regarding how the property is to be treated. if there is something in the contract about mainting it in proper condition etc, then you can again take action on the basis of breach. it may not allow you to specify that the dogs have to go, but you could either use it to ge them to leave, or at least clean up.