Prima Nocte (First Night) is a myth that during the Middle Ages, local lords could force a new bride to have sex with them on her wedding night. Quite aside from the potential for justifiable revolt every time a lord did this, it was flagrantly adulterous in the eyes of the Church and a good way to die in a state of mortal sin with your angry wife's knife in your back. In other words, it never happened. While rape, murder and all sorts of pillaging certainly occurred during the English invasion of Scotland, Prima Nocte did not. That Braveheart prettifies the chaotic brutality of medieval warfare with a 19th century power fantasy is a little disturbing.
The Bruce did not betray Wallace. A servant, Jack Short, betrayed him (and possibly a Scottish lord named Sir John Menteith) according to English chroniclers and 15th century minstrel Blind Harry.
The Bruce didn't dither for years while Wallace forthrightly acted. Being a major claimant to the throne, he had far more to lose, and was a bigger target, than Wallace. Wallace was not born poor or landless. He was a second son whose older brother would inherit everything.
Wallace was not a highlander. He was a lowlander who wore mail armor in battle. He wore neither highland tartan nor the blue woad of Roman-era Picts. He certainly didn't wear a kilt. Braveheart deliberately makes Wallace look like a rowdy peasant outlaw and not the medieval knight that he was.
Isabella the "She-Wolf of France" (She was King Philip IV (the Fair)'s daughter) was as formidable in real life as in the movie and then some, as her husband, Edward II, found out when she took a lover and had Edward deposed and murdered in 1327. But Edward I never would have sent his daughter-in-law to negotiate with a rebel and outlaw. That would have given Wallace far too much legitimacy. Plus, Isabella was only ten when Wallace died in 1305, so she couldn't have borne his child, either. The future King Edward III wasn't born until 1312, seven years after Wallace's death, anyway. Isabella didn't even arrive in England to marry Edward II until 1308, three years after Wallace's death and a year after Edward I's death. So, not only did she never meet Wallace, she probably never met her father-in-law, either.
Edward I never shoved his son's alleged lover, Piers Gaveston, out a window. Gaveston outlived him by five years, eventually being executed in 1312. We're not even sure that Gaveston and Edward II were lovers; Isabella and her lover might have drummed up the charge posthumously to justify her husband's murder.
For more fictional tales of Wallace and medieval Scotland, check out this week's Sunday Book Review.