Complex sentence: The emperor managed to convince Caroline that Queen Victoria was unlikely to allow one of her family members to marry a Grimaldi, but suggested Mary, his third cousin and sister of his good friend the 12th Duke of Hamilton, as a suitable alternative.
Split into simpler sentences: The Emperor managed to convince Caroline that Queen Victoria was unlikely to allow one of her family members to marry a Grimaldi. The Emperor then suggested Mary, his third cousin and sister of his good friend, the 12th Duke of Hamilton, as a suitable alternative.