I don't know much regarding lipstick plants, but I love ficus species. Your ficus benjamina looks nice and healthy. I agree with Will that it is best to just let it grow right now. This spring or summer (and I would lean towards summer if your springs rend to be cooler) when it warms up and the plants are growing more you can safely separate the individuals if you would like, even if their roots are really balled up. If the temps are warm, they will recover even if they only have a few roots each.
I use a garden hose sprayer to spray off as much excess soil as I can. Then I use something like a chopstick (anything similar will work) to help tease the roots apart. If needed, I'll alternate back and forth between the sprayer and the chopstick until separated. Then you can pot them back up as you please.
Mind you, I grow mine outdoors the majority of the year and we are pretty warm March through October/November. If you are going to keep yours indoors, once you separate them, you may want to try to provide some sort of bottom heat (like from a plant heat mat) in order to increase the chance of all of them surviving.
Like Will said, it will be stressful on them, but provided warmth they should bounce back easily.
