Wow, they really disregarded history completely.
Francis was short, shorter than Marry, plus she was 2 years older than him. They were also married when he was 14, and she was 16. Henry II died within a year of the marriage, Francis soon afterwards. Also, Nostradamus was already an old man by this point.
Francis also didn't have an older half-brother. He did have an older half-sister and a younger half-brother named Henry (who happened to be Mary's first cousin).
But after watching the first episode, it's pretty clear it'll be yet another, typical "let's make girls weepy and sell some music CD's" CW show.