Safe Re-potting ideas: My indoor ficus tree is root bound?

Trimming a little bit from the smaller roots shouldn't harm it, although probably not necessary. These are the feeder roots that take up the water and nutrients, so they are vital to the health of the plant. I hope you are repotting them in larger pots...if the roots are really crowded the trees are telling you they need more room. Putting them back in the same size pot will prevent them from getting all the moisture and nutrition they need to be healthy. You can tell if they are rootbound when the larger roots are circling the bottom and/or sides of the pot, often there seems to be more root than soil. You don't need to rinse off the old soil unless you are concerned that it is contaminated by insect larvae or something. Ficus usually go through an adjustment period when their environment changes in which they tend to drop a lot of leaves for a few weeks, so don't be concerned if this happens. As long as the plants are healthy they should adapt readily. Make sure to check them for bugs before you bring them indoors.

Potted Ficus Tree

Oh boy, get your ficus out of that bucket of water ASAP. It will not like being so wet and will drop leaves in protest.

Ficus can be soooo touchy. Don't trim any roots. Any little change will make a ficus drop leaves, and trimming roots will harm your plant.

I've repotted my ficus several times, and all I do is slip it into a new pot that is about 4 inches larger in diameter than the previous pot. Then fill in around the rootball with more potting soil. Those little roots you mentioned will reach out into the new soil. This method disturbs the plant as little as possible, and when you're dealing with fussy ficus, you want to disturb it very little.

I hate the tree pose