If Alexandra had married Eddy, there would have been just as strong a possibility of her producing a haemophiliac heir as there was when she married Nicholas.
There have been three widowed Princesses of Wales in all. The first was Joan of Kent, widow of the Black Prince, who became mother of the reigning king little more than a year after her husband's death. The second was Katharine of Aragon, who married Arthur, Prince of Wales, and then Henry VIII. The third was Augusta, widow of Frederick, Prince of Wales, who died in 1751 and was the father of George III.
Joan was already a widow when she married the Black Prince (she actually had quite an interesting marital history), and I think all her brothers-in-law were already married - will check.
Frederick and Augusta had no fewer than nine children, the last born posthumously.
Regards
Ann