Hi @raising_angel,
yes, only two displays can be duplicated – this is default Windows display settings behavior.
I suggest to use the Video Wall feature of spacedesk.
Open spacedesk Driver Console and check the Video Wall Mode setting.
Assign the Android tablets to Wall0.
Duplicate the spacedesk display and the other display.
For further details, please refer to our user manual, “Video Wall Configuration” topic (https://manual.spacedesk.net/VIDEOWALLCONFIGURATION.html).