I have the problem where my two map layers overlap each other, meaning that part of the map is hidden by the white area of the other layer. Thus I need to cut the excess white area to let the bottom layer show.
From what i see on your screenshots, you have lots of binary land registry tif files. Try creating a vrt to group them into only one layer.
To make vrt
gdalbuildvrt tif_images.vrt *.tif can be useful should you go through the osgeo shell.
When you have done that, you will have only one config to do for all images. From what I see, white is 0 color and 1 is black color. You just need to pass your 0 color into a transparent color to get rid of your white areas.
Bonus will be that you can then put an aerial photo below and see your registry lines on top :)
Extra ref : http://www.gdal.org/gdalbuildvrt.html