I have 3 week old twins who are currently on Enfamil Enfacare for preemies, they were born at 36…

I have 3 week old twins who are currently on Enfamil Enfacare for preemies, they were born at 36 weeks. Our pediatrician wants them to stay on this formula for at least 6 months even though one of the twins is up to 6lbs and experiencing reflux with the formula. The pediatrician prescribed baby Zantac instead of suggesting switching his formula. Any suggestions on switching from the Enfamil Enfacare to the Enfamil GentleEase? Only one twin is experiencing the reflux and I just don't want to have to medicate a 3 week old infant if changing his formula can help.