Im 19, my brother is 13. Whatever happens it sure wont be happening anytime soon. I am great friends with my cousin, he's 20. We've done MDMA and smoke a lot of pot. And same with another of my cousins, 16. We all drink and smoke occasionally.
Im not sure about the younger one doing E's. She's very mature and if she was do to it i know she would think about it in depth before hand. I would like her to, maybe in the future, but i wouldnt pressure her to.
As for my brother, I would like him to. A good friend of mine did Es with his brother with us last year and they had the most amazing time. This was in student accomodation. Later they went to their own room and talked and opened up so much to each other. Things like that make me want to do it with my brother. Obviously im not gona do it just for the hope of something like that. I am pretty close to him at the min and hope we will still be close in years to come and maybe something like this may happen. I'll just have to see how he turns out.