I would not book a grand villa. One problem with renting points is that you are set in stone. You want to make a change? You really cannot. RENting DVC can be a wonderful way to save money on lodging, but it can be tricky, and I firmly believe that folks who want to do this be very sure of their dates and travel party.
My family travels often as extended family and we do share space. FOr the most part we all can manage staying together, and have no issues, but if your travel party is not used to sharing space it can be an issue. WHen my DS and DDIL travel with us they get their own room, no matter how big our suite is. The rest of us appreciate this as well, My son needs down time without all of us, and his wife does as well. Having that level of privacy is important to them. I feel strongly that if folks are not used to close spaces they should not practice on vacation, and never on a WDW vacation. The parks can be very overwhelming and if it's crowded they can be stressful, so some people just need to get away from everyone once they return to the resort. That is not going to happen in many of the DVC villas.
I suggest that you cost out three rooms in a nice moderate. I think that POR is a nice resort with teens, but I think they might like CBR as well.