Refiners has a good point here, they will do what they want anyway, but ground rules should be set, and also, what they do sets example for younger, kids are young and like little sponges, they soak up everything they see.
This is a very difficult decision. Yes I went through all of this, yes I had girlfriends, and boyfriends stay in my home, you do live through this, I always thought I would rather have them here under my roof then elsewhere. I wasn't comfortable at first about this. This is so hard, because sometimes young ones being young tend to go from one relationship to another, to find that person who they eventually want to be with the rest of their lives, and sometimes, not always they seem to bring home all of their potential mates.Then you could end up having many boyfriends/girlfriends staying in your home. We sometimes think the first boy/girl they go out with is THE ONE, but doesn't always work that way. I believe birth control and condoms are a must, but I believe it takes at least 3 months for birthcontrol to work, that is what we were told by doctor. Takes awhile for it to go through your system. Then when all is said and done, you go through it with your next child, if you let one do it then the others expect they also can do it. JUST FOOD FOR THOUGHT, the decision really must be yours, it is your home. Yes we must remember what it is like when we were teenagers, and times have changed through-out the years.