I would not bother the dried yolk remains at all. It will fall off when on its own. If the chick is not doing well do separate it and give extra V&E in the water. Your chicks actually hatched a bit before it was ready or development was slow in the shell. It will take awhile to catch up or it just may be a weak chick and will always be smaller.
It is hard when you first start out but there are some chicks that just don't make it and we all need to be prepared to loose some. They can be weak for many reasons, genetic or some sort of bacteria or weak immunity. It is important to let the weak ones go if necessary. You want to breed hearty and healthy chickens that will thrive and pass those good genes along to the next generation.
