You will get 4 Chatterfang tokens and no Squirrel tokens.
As you resolve, Saw in Half, you observe its directions one by one. Chatterfang is destroyed, and despatched to the graveyard. Then you’ll create 2 Chatterfang tokens, however Parallel Lives has a static means that creates a substitute impact, changing the creating of two Chatterfang tokens with creating 4 Chatterfang tokens.
Although Chatterfang additionally has a substitute impact that may exchange making a token with creating the token and making a squirrel, there is no such thing as a Chatterfang on the battlefield on the time you might be making a token right here. The authentic one is within the graveyard and not one of the token ones have been created but. The new tokens will exist too late to do something right here:
614.4. Replacement results should exist earlier than the suitable occasion happens—they’ll’t “go back in time” and alter one thing that’s already occurred.