Currently, to build 'dlnetwork' object, network must contain only one input layer. Hence, in current framework you cannot convert your network with two separate inputs into 'dlnetwork' object.
However, you can use CombinedDatastore or can create your custom layer which is able to take multiple input. You can follow this link to get an idea how custom layers can be written.
You can also leverage this link to create your layer graph and then convert that into a dlnetwork object.