keep it light, it also means if you will life in the same roof if not, don't see why hold back, you will need to work on this lightly not too hard a lot of teasing, go a litle harder on they friend, if they become jealous maybe you will ahve something to work on, but the main here is work on they friend, and remember girls talk possible if you do pretty well and bag then really good the news can pick sis's interest