Family Echo automatically orders children in order of birth. If he is third, he must have the wrong birth date on the tree. Sometimes, though, in order to show more family members at one time, it reverses the order of all siblings. You don't need to fix anything if this is the case. If you have no birth date for him, try giving him one that makes him older than all his siblings and then delete it if you don't know his actual birth date. I'm guessing it might leave him as the oldest sibling.
