Carol 1 came to the Romanian throne in 1866 after the place coup lead to abdication of the prince before him. He had one child-- who died at the age of 3. The hopes of the royal family rested with Ferdinand, his nephew.
Ferdinand would marry Marie and would have six children, Carol II would have two children, Carol Mircea, who would have been King had his parents marriage not been annulled, Carol II would marry Helen of Greece who would have one child, King Michael of Romania, who has only daughters.
The sisters of Carol II are not a part of the extended Romanian Royal family rather-- one was Queen of Greece, and did not have children, and the other two Queen of Yugoslavia and Archduchess of Austria respectively. Carol II's brother Nicolas would also not have children.