The idea comes from a Russian course book I use in my teaching,(actuaaly, I copied the empty family tree from this book)and created a similar English worksheet. My pupils loved it. The single statements about the family members don´t give them too much information, so it was interesting and challenging for them to find out who is who. So solving this task is not only a good vocabulary practice but a serious reading comprehension at the same time. We can also give extra scores for those who can finish their job in a given time. Competition always motivates students! One more comment. Be aware, the lines that show relation between the members are important too.