A more expensive but faster and more accurate way would be to install lead-follower software in the VFDs and set up the VFD with the speed input signal as the lead. The others would then follow accordingly.

The suggestion of putting multiple motors on a single phase VFD is a good one if you are starting from scratch and, importantly, if speed regulation and syncronization is NOT important. Motors configured this way are free to wander within their nameplate slip speed range depending on individual loads which can lead to poor speed control if individual motor loads are different.

When sizing the variable frequency drives and motors, consult the manufacturer for any derating considerations regarding ambient temperature and altitude. Typical values are a 2% current derating for every 1°C above 45°C, and a 1% current derating for every 100m higher than 1000m above sea level.

The 2,000 rpm max speed almost surely isn't an exact limit or absolute number like the speed of light or pi. In other words, it isn't going to be a case of 2,000 rpm OK and 2,001 rpm the fan explodes! Limiting the maximum frequency of the VFD, which can be set from the keypad or using the A-B software, is going to give an accurate enough speed limit for this purpose. If you want, your variable frequency drive can be set up with the motor nameplate full load speed, and it will internally calculate and display the motor speed taking into account slip, percent of rated load, motor current draw, and so on. This answer will be quite accurate - certainly close enough for your purpose. (But remember to inlcude the ratio between the motor speed and fan speed if necessary.)