I tried to add with my Brother MFC-J6520DW however every time I try to print a test page or print something from the preview box it says that the preview interface is crashed.
I tried to print even disabling the preview printer but it doesn't work the same

I understand that you are still working on it but could be possible to catch the exception and log the error instead? so that this could be useful for us to help you.
Even if not at full feature could be this be fixed for brother printers? It would be super nice to have a minimal support for Brother printers at least via this way because the normal support is still not available.
best regards