I hate to say it, but locks on the doors may be an option...or one of those door bell chimes that stores have. You know, the ones that go off when the door is opened.
I can see the make-up, it's cool. I was forever getting into my sister's when I was younger. She's 9 years older, finally my mom bought me some "play" make-up and my sister gave me make-up lessons. That cured me.
Unfortunately the things of the older girls is always going to be tempting and I'm not sure if you can "level" everything since it's silly to give a 5yo an ipod. Maybe she can buy time on/with them for good behavior or chore rewards. She's in Kindergarten? Maybe good days get her time on the electronics of her choice?
I also pick up on your use of "my step-daughter(s)" vs. "my own daughter". I'm not sure how your family structure is, but it struck me as odd and if a complete stranger picked up on it, you youngest maybe acting out because she is feeling it too. I have a step-sister, but I never referred to her as that, she was just my sister. My parents never used "step" either. You may need to iron this out with your kids and husband and whomever else is in your kid's life (my sister's mother was not in the picture).
That said, she is 5, very little impulse control. "Not yours, Don't touch." was a very common sentence in my house while my daughter was that age. We even watched Beauty and the Beast, the scene when she sees the rose had my then 4-5 yo chanting "Not yours, don't touch!"