Which of these species is least related to the other three?
Although all four species belong to the dog family (canidae), coyotes, dogs, and wolves belong to the same genus (canis), and are so closely related that they can and do interbreed, which results in fertile offspring. Foxes belong to a separate genus (Vulpes), and are more distantly related.
The canidae family includes different dog-like mammals, both extant and extinct. A mammal belonging to this family is called a canid. They can be found elsewhere on our planet except Antarctica. The domestic dog is one of the most widely kept domestic animals in the world. Some other canids can also be domesticated, but most of them live in the wild.