Crumbly biscuits are usually caused by too little moisture or too much flour. If you think that this is the problem, try toning down on the flour just a little bit. I also add an egg to help bind ingredients together, which helps give the biscuits more of a stability and not be so crumbly. That said, it's also possible that you are over-baking the biscuits; gluten free drop biscuits are finished baking when they're slightly firm and have turned a light golden hue.