The marriage of Charles Brandon and Princess Mary is shown shortly before the birth of Henry Fitzroy. However Charles Brandon and Princess Mary were married in March 1515 and Henry Fitzroy was born in the summer of 1519.
Bessie Blount is shown being pregnant with her son Henry Fitzroy when Princess Mary is an infant. In reality Mary was born in February 1516 and Henry was born in June of 1519 so Mary would have been 3 when Henry was born.
When the court hears Bessie Blount go into labor Thomas Boleyn tells his daughter Mary to take her sister Anne and help Bessie. He calls Mary Elizabeth though which was the name of his wife Elizabeth Howard.