meaning in context - Difference between "kindly" and "please"

Manager to player

1. 
   

   
   

   Kindly practice every day

   
   

   
   


2. 
   

   
   
   

   Please practice every day

   
   

   
   

Teacher to student

1. 
   

   
   

   Kindly wipe the blackboard

   
   

   
   
   


2. 
   

   
   

   Please wipe the blackboard

   
   

   
   

Student to teacher

1. 
   
   

   
   

   Kindly give me a blank paper

   
   

   
   


2. 
   

   
   

   Please give me a blank paper

   
   

   
   

Sister to brother

1. 
   

   
   

   Kindly pass the butter

   
   

   
   


2. 
   

   
   

   Please pass the butter

   
   
   

   
   

Which is correct usage in the above contexts?