Cousins,
No Sinclair twins that I know of in our Islay line. But regarding twins, identical twins are a nonpredictable act of nature, and 2 sets or more in a family is a co-incidence. They must be distinguished from fraternal twins that depend on the mother ovulating twice in a month, a tendency which is familial. One could inherit this tendency from their mother, or they could inherit it from their paternal grandmother, in which case it would have "skipped a generation". There is a country in Africa, maybe Ghana but I'm uncertain, where the incidence of twinning is far greater than the rest of the world's population. Other than this I have never read of an increased incidence amongst others, Scots or Sinclairs, dynamic as we all are :)
Connie Sinclair
Nurse-midwife