When Colonel Brandon tells Elinor he once loved a woman who resembled Marianne, but she had to marry his brother, who she did not love, or him her. Then she had an affair with someone who was not Colonel Brandon and had an illegitimate daughter. Then I can't remember if this woman was divorced or dead, but the girl became Colonel Brandon's ward. Are we supposed to believe this? Elinor is happy to believe it, but it sounds like a whopper to me. I would want to have a good look at the girl to see if there were any family resemblance.
Colonel Brandon challenged Willoughby to a duel, but neither of them were injured. So I suppose, Colonel Brandon having made the challenge, Willoughby had choice of weapons and chose pistols. That would make sense because Willoughby spends a lot of him time shooting, while he would have had little practice with swords. I suppose they only had one shot each, or maybe Willoughby only had to submit to one shot to retain his honour. I could understand Colonel Willoughby doing this for his own daughter more than another man's.