Watch the Multi-Finger Free Stroke Exercise online guitar lesson by Andrew Leonard from Beginner Method for Classical Guitar
Here's a simple multi-finger free stroke exercise. As you can see, we are still in the "My Favorite Right Hand Exercise" position.
Be aware that when first learning, students sometimes have trouble getting both notes to sound at the same time. The solution is usually to slow down a little, double check that both fingers are placed at the contact points, recheck your knuckles are over the strings, and then play.
I like to think of this approach to practicing as "correcting the mistakes before you make them". I think practicing with this mindset leads to quicker and better learning.
Next, we'll add the use of P (the thumb) and fingers at the same time to our right hand classical guitar technique.