Difference between parsley and coriander(cilantro)?
Coriander leaf/cilantro looks VERY similar to flat leaf parsley. When I have both at the house I sometimes resort to smelling them to know which is which. 

Cilantro is very strong smelling, and you'd definitely change the flavor of the dish if you left it out.

Flat leaf parsley is significantly more subtle and has a much milder flavor and scent. It is not flavorless, and in a recipe that calls for a lot of it, you'd really be missing something by leaving it out.

When you've got a recipe that calls for both parsley and cilantro, you're definitely going to be more able to taste/smell the cilantro more than parsley, but they'll both contribute different notes. If you have to leave one out, leave out the parsley, but don't try to make up the volume with more cilantro, as you may wind up overpowering your dish. Just leave the parsley out and proceed as normal.

Do not use curly leave parsley in anything--it is tough and virtually flavorless. It is ONLY a garnish and not worth wasting your time on.