Sisters Princess Alexandra, the future Queen of the United Kingdom and Princess Dagmar of Denmark, future Empress of Russia. Hence the similarities of their sons, King George V and Tsar Nicholas II. Actually Alexandra was the Empress of russia.
King George V and Queen Mary with their 6 children. Edward [Prince of Wales later Edward Albert- later George [father of HM the Queen] Henry, Duke of Gloucester, George- Duke of Kent, Princess Mary- the Princess Royal and Prince John who died in his teens
LtoR Children of Prince Andrew Greece-Denmark & Princess Alice Battenberg, Germany: Princess Sophia Jun Nov , Princess Cecilia Jun Nov , Princess Theodora May Oct & Princess Margareta Apr Apr Greece-Denmark.