Question

derive the 1st law of motion from the second law of motion​

Answer 1

Consider a body of mass 'm' moving with velocity v. So we can state the first law: A body will remain at rest or constant velocity unless a force in acted upon it. A body continues to be in its State of rest or uniform motion along line unless it is acted upon by some external force to change the state.

Answer 2

The three results are independent in their initial conditions, and situations are different.

I am explaining, just after you learn what force is from second law, now whenever you are applying force to some body, its the third law that makes you believe the object is also applying the same force back, so during the application if second law, we have to consider the third law.

I hope that this helps you