I dont think that would solve anything I'm afraid, except that adding more fish will only make your problem worse. I think that the reason they're not that active is simply because they're not feeling happy/comfortable in the tank.
I think the main reasons the fish dont feel too comfortable will be because
1. Its too crowded (this depends on the size of the fish right now, but I'm guessing they're not all too juvenile anymore, meaning the tank would be crowded)
2. The dont have hiding places or any places to get away from the other fish.
A 3. might be the water levels not being ok making your fish feel sick. But I dont know about this one seeing as you dont have test kits yet

If you've kept up with your water changes though (about 50% a week) they will probably be fine.
The best thing to do I think is to take back all the fish to a shop near you (if they'll have them back) and start pretty much from scratch. Do some research on what types of fish you want (for example, if you want to keep the rams, do a search either on this forum or google, and find out how many gallons of room they need and how big they will get ... these are the 2 major questions you want to be concentrating on).
I'm sure that if you add some plants, wood and/or rocks to create a more "wild like" feeling for them, they'll be doing a lot better as well

However, sooner or later the fish Will grow to big and die coz of stress or because their insides got too big to fit inside their body.