is it possible to get fuller cheeks without fillers and just with cheek yoga exercises that make cheek muscles bigger?

The gold standard today is to use cheek fillers to augment the face.  This is an excellent method with proven safety. Best, Dr. Karamanoukian

Not really and certainly not uniformly. Some people will claim that they got "bigger" muscles from chewing gum but this would be more in the jawline, not the cheeks. There's no great way to do cheek exercises to make them larger. "This answer has been solicited without seeing this patient and
cannot be held as true medical advice, but only opinion. Seek in-person
treatment with a trained medical professional for appropriate care."