i think that each placement in the family has its pros and cons.. and obviously Hashem gave us the position in the family b/c thats what is best for us..
i think the oldest does have alot of responsibility.. but they are able to boss around the younger siblings to do alot of things for them..
i think the youngest has it the hardest b/c everyone thinks they are the most spoiled.. therefore the older siblings make sure that the parents give them less then normal just to make sure that they arent spoiled.
and the middle basically has it very good. they arent weighed down with tonz of responsibility like the oldest and they arent bossed arnd like the youngest..
so basicaly the middle is the best placement according to me.. and hterefore they should help their older and younger siblings!!