How can I darken the stain on my wood tables without stripping them?

You could try gel stain. It can go over other finishes. Test it in a small inconspicuous spot and see if you like it. :)

I love gelt stain for this. It's pretty easy to use. You can either brush it on and use the brush to pull off the excess, or you can use it like normal stain and wipe it on, then wipe away the excess. I find that it dries much faster than normal stain, so you can't let it sit as long. It needs to be wiped pretty quickly.

If your living room tables are a LIGHT oak a gel stain will work. You can go darker but not lighter. You could try a test area in an inconspicuous spot to make sure you are getting the color/finish you want before you redo the entire table(s).

It depends on the current finish. You might have to degloss first. If you don't, then scuff with fine steel wool and clean with denatured alcohol. Then you can stain with a gel stain.

As Kathy states it really depends on finish/sealer that was used whether it will even take a stain or if you need to remove the sealer first.Old saying"the shinier the finsh the more prep work needed".