I'm an 18 yearold lad with a sister of 13. My parents split up a year ago and we both stay at my older brothers at the weekends. I often go out and get in late or crash at a mates house, and my sister would have a couple of friends stay over. Over the last few weeks upto 4 of her friends would stay and my brother has been letting them drink and smoke the oldest is 14 but the youngest is only 12. The girls all think my brother is really cool and even though they are young, in there own way they flirt around him who seems to encourage them. In the mornings they walk about in short nighty's or just a pj top showing their knickers I'm sure they don't wear bras either. I find it embarrassing but I can see my brother watching them which makes them worse as they will bend over in front of him, he must be able to see down their tops. The two 13 yearolds were play fighting him and it didn't look right the way he touched them at times. I saw him with one hand on one girls bum and I'm sure he put a couple of fingers inside her knickers and slid them between her legs, while the other was being pushed away with his hand on her t***. Neither girls were bothered by it, I could see they liked it even encouraging him. By far my biggest worry is what I saw last weekend. I got home late so let myself in very quietly, I could hear a faint noise coming from the kitchen and was totally shocked when I saw the 12 yearold sitting on the work surface and her knickers were lying on the floor, my brothers head was between her legs. The girl saw me looking and gestured for me to say nothing, the following day she even said to me I could do the same to her but I said I'm not interested in girls her age, although it did excite me as she was really enjoying it, i guess she is very mature for her age. I spoke to my sister about some of the touching I've seen but she is not bothered and calls me a trouble maker. Although all the girls are more than willing to do all this stuff and happy to stay there I don't want to see him get into trouble if they tell any of their other friends.