I can't believe there's someone who brushes her kid's teeth while they sleep. Hilarious! My son would NEVER stay asleep thru that.
First, use the Orajel toddler toothpaste. It'll say on there "Safe if Swallowed." Second, give your son TWO CHOICES. "Do you want mom to help you brush your teeth, or dad to help you brush your teeth?" We do this with almost EVERYTHING with my son. "Mom clip your nails or dad clip your nails?" "Walk to your bed or me carry you to your bed?"
So try giving him those two choices. Whomever he chooses to help him, I let my son brush a little on his own (he likes to push the button on). Sometimes, I brush my teeth with him. We both brush on our own for a little bit. Then I put my toothbrush down and help him brush. Sometimes I sing to the tune of Row Row Row your Boat "Brush Brush Brush your Teeth, Brush your Upper Teeth .... Brush brush brush brush, brush your upper teeth." Then I sing again while he lets me do the bottom teeth. If I need to, we'll sing the verses again.
Other times, I've told him to roar like a lion.
When he was about your son's age (he's 2 now), I'd even let him brush MY teeth with MY toothbrush, so he could see what goes on when he brushes in there. That being said, maybe give him a mirror to see that he gets all the "yucky germs" off of his teeth.
Good luck. nd if worse comes to worse, take him to the dentist. If he HATES it there, then later you can threaten "Well if you don't brush your teeth then I wil have to take you back in afew weeks. If you DO brush your teeth, we don't have to go back for another year."