Not so sure about that. Some of those nieces and nephews are illigitimate too. And I’m not sure that either sister is married to their fathers.
Caroline has been married three times. The first marriage was annulled before she married husband no. 2. They had 2 sons and a daughter. He died and a few years later she married husband no. 3, who has the title Prince of Hanover and they have a daughter. Her sons would be legitimate heirs. Not sure about Stephanie, some of her children may have been born in wedlock or not. She may have a son, I pretty sure she has more than one daughter. Too lazy to google.
Caroline had a son/sons, but her husband that fathered them was killed in a boating accident.
Princess Caroline, Albert's older sister, has two sons and one daughter from her marriage to Stefano Casiraghi who died in 1990.
Pierre, Charlotte and Andrea Casiraghi attend wedding dinner for Prince Albert and Princess Charlene