Just found your mum on the family tree! Her father Harry C Ollenbuttel.His father Clarence Oxner Ollenbuttel.His father was William Henry Ollenbuttel - his father Henry Ollenbuttle (my 3 x g grandfather). I think I've followed the tree correctly - apologies if there's any mistakes!
I think the other people on this forum are all descendants of Clarence Oxner.
If you want, I'll email you my scanned copy of the family tree.