Yes all your brake pads should be replaced at once.
If you're replacing your front brake pads then both sides of the brakes should have new brake pads installed.
When you buy new brake pads they come as a set for both sides of the vehicle and all of the brake pads on one axle should be replaced.
Because if one side of the brake pads are bad the other side of the brake pads will also be bad.
Also it would be good to check the back brake pads as well and see if they need replacing.
If you haven't replaced the back brake pads and are replacing the front brake pads then the back brake pads should at least be inspected.
Usually the front brake pads wear out faster than the rear brake pads but sometimes they all need replaced.
Some vehicles have brake pads on the front and brake shoes on the rear and it's good to check them.
Also check the brake rotors as well and if there's cracks or warping then the brake rotors need replaced as well.