The app cannot control lashups. One engine at a time only.
That is not entirely correct.
The new F-units each have a Bluetooth module, all with the same BLE ID (Bluetooth Low Energy). The rear A and B units have a "slave" ID and the lead A unit has a "master" ID. So with the Universal Remote and the LionChief APP, you can run an ABA configuration. It will control up to 3 engines total in this configuration. If you have the AA set and both B-units, the BLE will not control all 4. Only 3. This is a BLE system limitation.
Keep in mind that this is only for same-roadname engines. A Santa Fe A-unit and a NYC B-unit cannot be run together via Bluetooth.
Hope this clears it up.