Best way to handle tent ask for a dog.

[Kevin Velarde]

I have had this tenant for a year and he and his wife and 3 children have been fantastic. Their lease is about to expire at the end of this month. I just got a text message from them asking to add a pet(small dog) to the home. I live in the back house behind my tenants and don't want things to get  awkward if I refuse .  I know their children have wanted an animal for a long time. how would you guys best handle the situation. I'm not too happy about adding a dog to the unit.

Text message from tenant: 

Hi, sorry to bug you but I wanted to ask you if it will be ok if we took in my mother in laws small elderly dog he is about 12 years old and is completely house trained, she needs to place him and asked us but I wanted to run it by you 1st. Here is a picture of him so you can see he is a small dog.

Please advice

Regards