Have you ever noticed that in romance series featuring male siblings, you can often find the same character types? This seems true regardless of subgenre. This isn’t a comment about quality, by the way. Sometimes, these characters are done really well, so that they stand out regardless of how similar they are “on paper” to others in the genre (they’re not really “stock” characters at all), but other times, they read like the author is following romance writing by the numbers.
In contemporary, I am just finishing up Susan Mallery’s Irresistable, which features a hero, Walker, who is dark and mysterious, has a lot of inner demons, and can’t trust himself to bond with women or children. He has an (I think) older brother, Cal, who is serious and hard working and carries the family’s name on his shoulders (in Delicious), and another brother, Reid, a retired major league pitcher who is a footloose womanizer, determined never to settle down (Sizzling). Kathleen O’Reilly’s Sexy O’Sullivans series gives us the hardworking, responsible eldest (Gabe, in Shaken and Stirred), the middle brother with tragedy in his past who cannot bond (Daniel, in Sex, Straight Up, a book that was so much better than its title, BTW), and the footloose, womanizing, never get married youngest (Sean, in Nightcap). Then you have Susan Elizabeth Phillips’ Bonner brothers, and while the brothers’ places in the family tree don’t mimic the structure outlined above, you have the same three basic characters: Cal, the pro quarterback, never-gonna-settle-down womanizer (Nobody’s Baby But Mine), Ethan, the serious one (his is the secondary romance in the next book), and Gabe, the dark tortured soul with a tragic past (Dream a Little Dream). (How about Nora Roberts’ Quinn brothers? Haven’t read this series…)
In historicals, you have Loretta Chase’s Carsington series, about three brothers. Benedict (Mr. Perfect), who is the eldest, is the uptight, responsible one. Alastair (Miss Wonderful), who is a war veteran, carries dark demons and fears he may never be able to have a normal relationship, while Rupert (Mr. Impossible) is the youngest: goofy and womanizing and determined never to settle down. How about Julia Quinn’s Bridgerton’s? I am pretty sure you can find all three characters there (although they may not all be Bridgertons).