An End device can only join a parent router or coordinator. Once joined to that parent, all data sent or received for that end device is routed via that parent.
If you want to send data to a specific radio or node on that network, then you set the Dl and DH to match the SL and SH of that node.
NOT not use the DL and DH fields for routing of data. The DL and DH fields are ONLY used to provide the last radio or node in the network that is to receive the data, pass it out its UART or do something with it. The routing of the data is done automatically.