Please put a location and or zone next to your name so we can help better, as some advise depends upon your location.

A North facing window is not enough light for a tree, they need a South facing window to get through the winter. A West window will keep them alive but it's still not enough light. You may have to add lighting to give the plant enough. The white on the stems could be latex sap or mealy bugs, it's hard to tell. The spots look like oedema ( when the plant has too much water in it's stems and leaves and it gets too cold causing cells to burst) Some of the leaves look way too dry also. It could also be accumulated salts causing the brown leaf tips. The next time you water do a full flush. You will probably need help to get it to the shower but give it a really good soak. Do not let the water get too cold. When it's done draining, tilt the pot a few times then move it back. (hopefully to better lighting)

I agree. Probably too much water and not enough light.

How exactly do you water? In small sips or until it flows out of the drain hole? How often do you water? Never let the pot sit in the water that drains out.

As mentioned, a southern facing window would be much better. I have all of my ficus in southern facing Windows with the addition of grow lights.

Low relitive humidity inside also isn't the best for them. That'll also attract spider mites.

Mentha - done. I'm 7b, on GA/AL west of Atlanta.

My windows are all S or N facing, and the ones facing S are covered by porch roof, or not accessible. Other plants are doing surprisingly well in the N facing ones, including the umbrella plant that sits in my husbands "dungeon" (half his shutters are closed, and his N window is extra shaded), my room is much brighter, with some direct sun in the afternoon. It will have to be enough for now... I will look into grow lights.

Pretty sure we don't have mealy bugs.

Dave -

I gave the guy in worse shape a nice, lukewarm shower yesterday. Flushed the pot, as well. He looks happier. Until now, I was watering twice a week, in "small sips". I guess that's a no-no? I did my best to not let them sit in water.

What about re-potting/splitting them? Should I wait?

Only watering in small sips will likely cause salt build ups from tap water and fertilizer. If you must water in small sips, you should use distilled water.

It's best to flush out the soil every so often.

If you can't make sure you empty the collected water in the tray, use bricks or something similar to prop the pot up and space it off the tray. Just make sure the drain hole isn't covered.

Id wait until later in June to do any repotting or separate them.

Repotting means you'd be removing the plant from the pot, removing ALL of the soil, possibly root pruning and then placing into a new pot with fresh soil.

Potting up, on the other hand means you'd remove the root mass and soil leaving it all intact, placing in a larger pot and filling the bottom and sides with fresh soil. However, this method is no where near as good as potting up.