Dude, I'm sorry in advanced, but I'm going to break your heart... Those plants look like hell. The growth is limp, they are stressed to the max, they have never been pruned, and they are in pots that are too small, with probably low quality soil from a home improvement store. I hope you are at least using liquid fertilizer, if not I can tell you exactly what the problems are, poor quality genetics from bag seed, lack of fertilizer, and piss-poor lighting. I mean, that is really bad lighting. You need to be purchasing a HID High Pressure Sodium lamp. 250+ watts. You need a liquid fertilizer kit, bigger pots, high quality soil, and some real good genetics. I'm sure the pH is way off on that thing, do you have a pH meter? That is a bare necessity.
Maybe if you pruned off all that nasty undergrowth that is getting almost no light, it would encourage flowering. I would snip off at least the bottom 4 pathetic branches.
You need to do some serious research before you grow. Growing a plant is not difficult, successfully harvesting a dank crop off a plant is another story. 40+ Hours of research online is a bare minimum, 60+ Hours of book reading I would recommend as well. I like the Marijuana Horticulture Bible, Greg Green makes one, Jorge Cervantes makes one, and they make an excellent one as a collaboration, and that has Greg Green's name on it.
It looks like they are stuck in the corner of the attic, you need to build a real enclosure for them, and create a excellent artificial environment. Indoor weed is often better than outdoor weed because we can create the perfect indoor environment, and that is the goal. We are not all blessed with beautiful weather, year around. If you are so fortunate to be in an area with excellent year-around weather, you need to get your plants outside, and start using auto-flowering plants outside of the traditional grow season.
Some more issues I see, your lights are the wrong spectrum, flowering will take FOREVER like that, you need something that is 2700K, you have either 4100K or 6500K right there. What is the light cycle you are using? The plants need 12/12 to flower.
You should post some more details so we can at least tell you what is wrong.
But honestly, you should start over, and put a real investment of time and money into it before proceeding.