This is very simple, is it even possible to add in a unmanned mortar. Like any other unmanned object, it can only be controlled by UAV operator. When the UAV operator is in his computer, the mortar can go into the scope mode or artillery computer.
The ammo count would the only one set (roughly 6-8 mortar shells) before it is empty and unusable unless refilled by ammo support. The mortar can still shoot smoke rounds but that can be changed depending on what everyone thinks.
To move the unmanned mortar, it still requires two people to move the mortar with the two backpacks.