Yup, you can separate them, and in my experience it would be best to do so. In my first grow, I didn't have enough pots for my enthusiasm and had two pots with 3 plants in each, they can work together if they're the same strain they won't 'fight' each over, while if they're different trains they compete badly. At first they were alright but, later I couldn't keep up with their nutritional needs. I carefully separated them, VERY careful with the main root ball, lost a lot of the smaller roots as they were starting to get pot bound and the roots were intertwined with each other. After swapping them into their own pots and carefully nursing them, they passed through the shock and started growing again after about a week. I performed the transplant at around 3-4 weeks into veg (2-3 weeks as seedlings). Personally, I wouldn't do it to young seedlings as the shock may be too much but, I wouldn't wait as long as I did the first time. If I were in your current situation, they're only a half inch tall now, I'd wait until they have around 3 nodes going before I transplant, that way they'd have some strength and good green to help get over the shock. Just be VERY careful with the main root ball, try to save as much of the other roots as you can (those smaller ones are the parts of the root that actually take up nutes + water), use fresh soil, and water before tranplanting. Watering fairly heavily sort of drowns the roots and puts them into a 'sleep' mode. Do it in a darker environment, out of direct light, as roots do not like the light (doesn't have to be completely dark, just no strong direct light).
I'm not an expert, only on my 4th grow now, just hoping my experience helps, good luck, have fun, and remember, it all adds to experience!
