Training second dog

My first dog is almost 2 years and very well trained. Very good at holding positions, waiting, etc. I just got a puppy he is 4 months. I have started training him the same way u trained my first. I want them to understand different commands like if I want one to sit vs lay down etc. whenever I ask my puppy to do something, my first dog does it also. How can I differ the commands between the two? My first dog just gets confused.