[charrisTTI]

your program assumes that all the motors go exactly the same speed and stop/start immediately.

you need to take inertia of your system into account.

looks like a typo for the compare value of rot_encoder2: rot_encoder2 < 2 should probably be rot_encoder2 < 20 (in several places)

try evaluating each encoder value separately and turn the corresponding motor off when that encoder reaches the desired value.

you may also need to accelerate and decelerate the motors rather than just a hard stop and start to reduce overshoot.