symfony form builder constraints code example

Example: symfony form constraints

Other solution by using Expression Constraint for cases 1 and 2.
use Symfony\Component\Validator\Constraints as Assert;

// ...

public function configureOptions(OptionsResolver $resolver)
{
    $resolver->setDefaults([
        'constraints' => [
            new Assert\Expression([
                'expression' => 'value["Count2"] >= value["Count1"]',
                'message' => 'count2 must be greater than or equal to count1'
            ]),
            new Assert\Expression([
                'expression' => 'value["Count3"] <= value["Count2"]',
                'message' => 'count3 must be less than or equal to count2'
            ]),
        ],
    ]);
}
For case 3 you can use Assert\GreaterThanOrEqual constraint directly on Count2 field.

I guess your form doesn't have a binding object model, otherwise to read the documentation referred is enough and better because you could use these expression on your properties directly.