I didn't even know this was a thing. My FSIL offered that I could wear her garter. I was emailing with my Mum the other day and mentioned it and that I didn't even want to wear one, and she wrote back "funny you should mention it, I just asked my cousin where the family garter is"... Apparently she wore it and so have at least 3 other family members.
So I still don't really want to wear one (we're having a DW just with immediate family and going for lunch after courthouse wedding)... But is it really so expected? Is a family garter a thing in other families?!?