The are leggy for more than one reason:

-- two many in that pot
-- Not enough light and heat.
-- not been pinched off

I think what you can do now, to cut about 1/3 from top and see what happens. I think the are root bound and tangled . So not a candidate to be separated and re potted.

Basil is a heat loving , sun loving plant. So it is difficult to have it thrive indoor.

I bought it like that, anyway I do have it outside in the balcony with a lot of sun and heat as I live in a tropical country. I agree about the pinching, as I've said I had no idea how to harvest at that time. I'm afraid if I cut it off to a third from the top, it will die as the bottom itself does not seem to have any active growth points. Will it spontaneously start growing if I do cut off that third?

Take some cuttings (green stem only) and put them in a glass of water. They'll root, then you can pot them and start over. :)