I have seen W3 and W4 long ago but I am afraid that the problem will be elsewhere. Here are a few shots in the dark
First, IIRC, all diskettes following the second one in W3 were in XDF format. We can suppose that the situation in W4 will be similar. Therefore, if you got problems at the 12th diskette, the problem would not be caused by the format. I guess that the disk_12 is damaged and causes the installer to restart before the installer prepares itself for the restart. That's why the installation moves in an infinite cycle.
At any rate, both W3 and W4 needed BASEDEV=XDFLOPPY.FLT in your config. sys (I think it was basedev but I am not sure). Check it. eCS does not use this and it can still read XDF formatted diskettes. Most likely, Daniela's drivers know the format and need not the filter.
Second, IIRC, the "disks" on your CD are disk images. The xdfcopy.exe is an OS/2 program, which is able to copy an XDF disk image from one disk *or from an XDF .dsk file* to another diskette. You will need the filter xdfloppy.flt for it. But what to do next? I am not sure whether the classic disk image managing programs are able to operate the XDF formatted images. At any rate, you can try loaddf.zip from Hobbes, which should contain both loaddsk.exe and savedskf.exe. You can also try xdfcopy.exe whether it is able to create a disk image if it is able to read it.
Third, the unpack2.exe is an OS/2 program, which is able to unpack the "bundle". IIRC, if you have the filter installed, you won't see the "bundle", it will be already "unpacked", you will see individual files, and you will be said that the total size of the diskette is 1.8 MB.