You just can't grow more than one plant in a pot. Either carefully repot one, or kill the weakest. You can't hope roots develop, yet hope they don't interfere with each other at the same time.

I would imagine a seasoned grower would want to know what your PH is...it should be around 6.8.

When trying to figure out a problem, you have the eliminate what you know it isn't...like too high/low PH, or too much heat, or bad soil. If you have the basics down, then MJ plants wants to grow like crazy.

It shouldn't be a fight.

A good pot; decent soil without added ferts; a good light; a fan; some SuperThrive; low 80's temps; and PH6.8 water.

By the time you reach three weeks, you should have a little bush.

BTW, as long as you aren't adding extra ferts, Miracle Grow won't kill your plants. Some people actually like it. I've seen huge, beautiful plants grown with Miracle Grow.