two 15 HP 480 pumps VFD's Located in building 800 feed away. ( Pumps in a flood plane area) .
Is there a Problem running two feeders from VFD;s in same conduit the 800 Ft .
The reason I ask is I heard there could be a interference problem between cables in the same
raceway. They know they might lose the pumps but want to keep the VFD's out of harms way.
Yoopersup

If the feeders were twisted it should eliminate the cross talk but I am not sure how you do that unless you pull a cable that is twisted (like SER)
At the frequencies we are talking about you don't really need that much twist. You might be able to get a twist in each set as you are feeding them in.
Are you doing this all in one pull?

I wouldn't only be worried about crosstalk; I'd be concerned about the 800 foot distance between the VFD and the motor unless appropriate filters are installed.

Voltage drop will be tough too. figuring FLA at around 20a, you need #6 cu to keep the drop around 3%

1 conductors per phase utilizing a #4 Copper conductor will limit the voltage drop to 2.49% or less when supplying 30.0 amps for 800 feet on a 480 volt system.
For Engineering Information Only:
70.0 Amps Rated ampacity of selected conductor
0.2957 Ohms Resistance (Ohms per 1000 feet)
0.048 Ohms Reactance (Ohms per 1000 feet)
14.399999999999999 volts maximum allowable voltage drop at 3%
11.933. Actual voltage drop loss at 2.49% for the circuit
0.9 Power Factor

21 amps x 125% =26.25 round up to 30 amps for safety .