the depth of field (how much is in focus) is controlled by the aperture of your lens/camera, the bigger the number, the more is in focus
for example, if you set your camera to Ap (aperture priority) you can then change a number on the screen, make the number realy small F3.5 for example and take a pic of something fairly close with some stuff in the background at a distance, you will find the item in the forground that you focused on sharp and the background blurred / diffused
then set the number to a large number F20 for example and do the same photography, you will then see that the background is sharper too
the downside of this, is you will prob find the shutter speed was much slower when you took the 2nd pic ... so if your taking a pic of a moving dog for example, that makes it realy hard
its a balancing act to be fair .... you can up your iso (sensitivity to light) to make the shutter faster, the downside of this is a more noisy image (noticeable noise starts at 800 iso)
the other thing to bear in mind, is if the 2 dogs are the same sort of distance from the camera (eg chaising each other) it allows you to have a shallower depth of field and keep both dogs in focus
best thing to do ... is have a play, both in Ap (aperture priority) to understand how to get the right depth of field, and also in Tv (shutter (or time) priority), this allows you to control the shutter speed so you dont get a blurred dog, and let the camera balance the light by adjusting the aperture
if you get the hang of both of these, then you can play in manual mode
sorry if thats a bit techy
let me know if it is and I will try to explain a different way
Phil