I had the great pleasure of seeing the Assads in concert at the beautiful Weill Hall at Sonoma State University a few days ago. It's the third or fourth time I've seen them, and each time I wonder how they evolved to play in such different positions, as you can see from this picture, from their website:
Odair plays with the lower bout resting on his right thigh, the guitar held high, sometimes up to about a 45 degree angle, and his chin very close to and sometimes touching the upper bout. His right wrist is in a generally straight, neutral position. He is often on his tip-toes, swaying with the music, almost like dancing with the guitar.
Sergio, on the other hand, plays in a much more "traditional" posture. He uses a really high foot stool, his right forearm is almost parallel to his waist, and his wrist torqued downward much like you see in pictures of Tarrega, Segovia, etc.
They were both taught by their father initially, then had the same teacher, so I find it interesting that their technique is so different.
“People may say I can’t sing, but no one can ever say I didn’t sing.” --Florence Foster Jenkins