In OTL Isabella and Ferdinand had five surviving children and several stillborns.
OTL Isabella would likely be named as Juan
OTL Juan would likely be named as Isabella
After that, let's say Juana is instead Ferdinand, Maria is instead Alfonso, and Catalina is instead Pedro.
- Isabella (1470–1498) married firstly to Alfonso, Prince of Portugal, no issue. Married secondly to Manuel I of Portugal, had issue.
- A son, miscarried on 31 May 1475 in Cebreros
- John (1478–1497), Prince of Asturias. Married Archduchess Margaret of Austria, no surviving issue.
- Joanna (1479–1555), Queen of Castile. Married Philip the Handsome, had issue.
- Maria (1482–1517), married Manuel I of Portugal, her sister's widower, had issue.
- A stillborn daughter, twin of Maria. Born 1 July 1482 at dawn.
- Catherine (1485–1536), married firstly to Arthur, Prince of Wales, no issue. Married his younger brother, Henry VIII of England and was mother of Mary I of England.
OTL Isabella would likely be named as Juan
OTL Juan would likely be named as Isabella
After that, let's say Juana is instead Ferdinand, Maria is instead Alfonso, and Catalina is instead Pedro.