I believe it is much simpler to first try with the other "tekfwtool", and then the different "tektool":s, and if neither of those help, see if there is some other software fix.
As I suggested, you can also try if one of the "tektool":s manages to identify the chips, and if not, open it up and read on them. If you know what model they are, it should be able to modify "tekfwtool" or "tektool" to erase them.
Also, I find it very likely that you can't erase the flash without desoldering it.
Ragnar