It is an old post, so you might have found a solution, but I will still contribute nonetheless.
Have you tried to use a unit gain buffer beween the voltage divider and the servos?
Voltge divider - > Unit Gain - > Servos.
- Unit gain takes power from an external source to provide the necessary power and current to the servos.
- Voltage Divider set the voltage to whatever you designer it for and will remain almost unaffected by the servos tanks to the Unit Gain Amplifier. The unit gain takes a sample of the voltage divider an "forces" the same voltage to the servos.
Unit Gain Amplifier: You would just need an opamp and connect the negative pin and the output pin with a simple jumper ( No Resistance or other ) to act as buffer. This way, the motor resistance would not affect much the Equivalent Resistance.
The negative pin of the unit gain would also be connected to the voltage divider for the control of the voltage, output pin to the servo or servos ( Voltage at Vin would be the same as the Voltage at Vout thanks to the unit gain ).
Then what feeds the opamp ( +V and -V ) could be an additional power supply with higher voltage, like it could go up to 12-24v depending on the opamp specification, hence it could provide whatever current the motors would need. ( Bare in mind that the 24v would not go directly go the motors given it is controlled by the 5V input pin via the voltage divider )
This way you would not suffer from the Equivalent resistance off the voltage divider affected by your servos in your design, and could provide extra current to the servos from another external power supply which could go up to 24 Volts. You would need to get an Opamp designed for 24V of power and whhich does not release too much heat like in a linear region at 5V of operation.