wow, you are gonna have one hell of a jungle in there. Taking three out immediately is a start. Do you have room for fabric pots? each plant needs a minimum space of about a meter squared at it's full size.
Unless!!!!!!!!!!!!!!!!
you can also do a sea of green, or a scrog. You should look up scrog tutorials on youtube. It's basically hanging a rope trellis over the plants and tying them down to spread out the tops as they grow. You "might" be able to get away with it that way, but having so many plants in there is going to increase competition for nutrients, and increase disease pressure. If those are all the same strain, you can do it, if they are not the same plant you might run into nutrition management problems. Either way, your yield will be less per plant unless they each have enough room to stretch out.