The company said Carnival Cruise Line (CCL) and Holland America Line will take delivery of the ships in March 2018 and late November 2018 respectively.
It did not reveal prices for the new vessels.
The Italian yard is already building six ships for various Carnival brands.
The CCL vessel will carry 3,954 passengers and will be the twenty-sixth in the fleet.
It is a sister to Carnival Vista, due in spring 2016, from the same yard.
Holland
