If 5V was pushed into the AD0 of all the MPU-6050, then they all might be broken / damaged / no longer reliable.
Can you buy new sensors ?
You could also buy a 3.3V Arduino board.
How often do you want the data ? The I2C bus is slow and 14 sensors means 14 times slower.
What about a 3.3V Arduino board like the Arduino Due and the MPU-9250 in SPI mode ?