original: Together they had 18 children, of whom 11 survived to adulthood.
simplifications: They had 18 children, only 11 survived. 11 of their 18 offspring survived to adulthood. They had 18 children. Eleven of these survived to become adults. Together they had 18 children. 11 lived to be adults. They had 18 children. Eleven of them lived to be adults. They had 18 children, 11 survived to adulthood. They had 18 children in total. 11 of those 18 children lived to be adults. 11 of their 18 children lived to adulthood. Together they had 18 children. 11 of these 18 children survived to adulthood. Together they had 18 children, 11 of whom had survived adulthood.