I haven't btdt as the mother but do come from a family with a similiar situation. My grandfather's name was Stirling Eugene and my father's and brother's name is Stirling Edward. My grandfather continually called my brother the third though he was technically the second. It drove my parents crazy. Anyway, it's ultimately your choice and if your dh is fine with not using William than the family will eventually get over it. I agree, I wouldn't want a William when I already had a Willa. If they do ever bring it up I would explain to them (like you did here) that you feel you have already somewhat followed tradition by using the name Willa. GL!!