I have, well, rather my husband has, a brother and sister marrying a sister and brother. These are his parents, and of course, an aunt and uncle. This is 1939 - 1941, New Zealand. Thus his cousins from the other marriage have exactly the same ancestors as he has. One of my husband's brothers really looks as though he should be in the other family - he looks more like his cousins than his own brothers and sisters.
Jean