How do I get my new housemates to sign a roommate agreement?

Ok well to make a very long drawn out story a just a lil shorter, i'm going to set up the situation for you.... I'm in college ending my sopre year when i find out I will not be given housing the following academic year. Immidiately we search and find a brand new townhome being built right on campus (3 bed/bath). I sign the lease, I advertise that I have 2 rooms available, summer comes. My boyfriend tells me of a girl that he thinks has similar likes and is pretty much a homebody that is interested in my place, the girl (we'll call her A) does the application required by the realty company.........end of the summer is coming up. In the meantime (A) says she knows of an aquaintence of hers that was looking at the place. Girl (B) calls and we talk briefly about the room and other specifics, but most of importantly girl (B)'s mother and mine talk about everything. _________________________________ ok know that ive set the problem here it is: Moved in (ugh) and already there starts these little problems, (A) smokes in her room-that gives me headaches, not to mention its not good for my voice. (A) has guys in and out of the house all the time. regardless off whether or not the guys are just friends its just that I don't know them. she doesnt introduce them and you have to be careful who you let in your home. next thing you know you have been robbed by someone's friend of a friend of a friend that came by and saw what we had in the house. Girl (B) hasnt done too much to ruffle my feathers, the most problems that come from her is financial. Anyway since the lease the girls signed does not include utilities or any like "house rules," I took it upon myself as soon as I had signed my lease before the end of the year to make up a roommate agreement addressing what could and could not be done in the house, how long someone could stay overnight as well as the payment of utilities and services-(internet,cable). There was also a part in the agreement discussing the 3 parks in front of the townhome that belongs to us. These parks are to be divided one for each occupant or a guest of the occupant, (A) will pull up on the gr--which is prohibited by the landlord and let her guest park in her space and the 2 other spaces belonging to me and (B)...without asking! I addressed the parking problem with her but hshe as yet to do anything about when it comes to her friends parking in my spot or taking up all 3. So I talk to the girls individually and together after we have moved in and are settld. (A) says the part about alcohol and smoking is a problem and she would see what she could do before signing it....I said that was fine, after all this was just a draft...a basic copy (none of us are 21, so why she cant agree to that im not sure, lol). Girl (B) tells me she doesnt agree with any of it because she feels she is too old for a roommate agreement. did i mention im a year ahead of them and prolly even older than that than them.....so if she is too old so am i . her problem is that it is her first year off campus and she think she is grown. So after (B) says she isnt going to sign at all both of them say there is no need for a written agreement and that we should just go talk to eachother if there is a problem and adhere to "common courtesy"......UMM the problem with that is I dont know them so "common courtsey" to them may not be the same to me. I dont kno how they grew up, if they r use to nice things or not. There needs to be something saying that these are the rules, regardless of how flexible or lenient they may be. I dont know what my next move should be, I need an agreement that is not just verbal. HELP ME!