Hello dear cuongtran
The way to calibrate two cameras are the same to calibrate one. Take a look to the online manual
There are videos that let you choose the right values for cameras and projector. The only think that change with 2 cameras is that you should place them at the sides of the projector, with a similar angle with the projection line.
The advantage to use 2 cameras in "stereo mode" is that you can have lower angles than 1 camera or then "extended mode".
So.. be sure to have nice projection values and good camera settings, in according to the projector frequency and resolution.
If still not able to calibrate, please share a shot of your setup and a screenshot of David interface during calibration.
Thanks and regards,