It seems that you are using cables or adapters that are not being recognized on your system.
The use of adapters for different technologies may result on unpredictable behaviors. That is the reason why we highly recommend the use straight connections.
Also keep in mind that most of the time the adapters are from different manufactures and makes it more difficult.
Again, I would recommend you to try straight connection, maybe using somebody else monitor and report back.
We have 2 monitors connected to a D54250WYK NUC and it is working just fine, but we are using straight connection to the HDMI port and Display port outputs.