[Importing Brushes]

I was also trying to figure this out and I came across a solution, albeit a long process, but it works for Kyle's, Frenden's and any other brushes you might like... aside from I think blender brushes.

 

So, in PS select the brush tool, then select the brush you want to make into a .abr brush file. Open the brush/brush presets toolbox on the right and with the brush you want to make usable in Affinity, click the "create new brush" icon in the lower right. Name the brush, I named mine the same as Kyle and Frenden had them named, save the brush.  It is then added to your brush menu in Preset Manager.  Repeat for each brush you want to use in Affinity.  When you have all the brushes you want, or just one that you wanna try out in Affinity, open the Preset Manager for brushes by clicking the little arrow beside the brush tool icon.  Once in Preset Manager change the "Preset Type:" to Brushes, you should now see all of your newly saved brushes in this dialog box.  Click or Ctrl/Cmd +click to select one or many and then choose "Save Set...".  Save to a location that works for you.  Open Affinity Photo Click on the little icon with 4 lines and a small arrow ( this is all the way to the right of where the Brushes Tab is located).  Then click "Import Brushes".  Once it finishes importing them, you will have to select the file with your newly imported brushes from the Brushes Tab, use the drop down menu and select your new brushes.  Enjoy!

 

Hope that is helpful.