Hi tobi, Sorry, I haven't see your reply before today.
You are right, awf-gtk(2|3|4) are using the same source. Yes, multiple major GTK versions can be coinstalled.I have created three packages because if I create only one source package that depends on libgtk-2|3|4-dev, I think I will get the following error: Missing build dependencies: libgtk-4-dev.
So I prefered to create three independant packages. This has been accepted on Fedora and openSUSE (my Ubuntu PPA says also ok).
Thanks