Hi,
I think that we may have others with this type of MODY,(MODY 3) not sure it's quite as rare as has been suggested to you as it is the mutation that causes 70% of MODY. Having the right diagnosis will really help you.
I expect that you've seen the Exeter site but I'll give a link to it . You can if you want to then follow up the research papers on this type of MODY
http://www.diabetesgenes.org/content/hepatic-nuclear-factor-1-alpha-hnf1a
The blogger, Jenny Ruhl has MODY and you might like to read her info on it:
http://www.phlaunt.com/diabetes/14047009.php
The mutation is on chromosome 12 and you can read a bit more about the genetics of it here. (some of the links are specific but very technical
http://ghr.nlm.nih.gov/gene/HNF1A
Normally, (there are a few caveats) genes that are not on the X or Y (sex) chromosomes can be inherited equally by males and females( basically you have pairs of chromosomes and receive one from father and one from mother) so it may be chance that it is only the females in your immediate family that are affected by this This is something to talk to specialists about. (the people at Exeter on the first link are world experts)