Problem with Flushing

I have two girls in a 6 gal DWC tub. One is almost ready to be flushed and cut down. The other has a while to go. The roots of both are in a mess together, so separating into separate tubs is going to be a problem. What is the best route to harvesting both at peak times with the least amount of damage?

You're going to have to find a happy medium, let one go long would be the best bet. Then harvest the other a little early and you've got two different highs from the same grow.