Agreeing with nikkiolie.
For one it looks like all of the characters you are doing have different colored hair and it's better the be accurate to that. Whenever I see someone who doesn't have the same hair color as whoever they are cosplaying it seems really half-assed to me (Not to sound rude, just how I feel). Also having a wig to throw on whenever saves a lot of time in styling. Even if it is just long straight hair you have to brush it and maybe put some stuff in it to give volume.
Even if your hair is long you can get it under a wig with a wig cap like nikki said. There are a lot of tutorials on cosplay.com, deviantart.com, and even youtube. I'd suggest one, but I have really short hair so putting on a wig cap is super easy for me :B
Good luck with your stuff~