I’ve done recorded videos, showing off the Shadow Dragon characters. While Navarre and Minerva share movesets with Lyn and Camilla respectively, they do have unique specials, animations, and of course voiced lines and statlines.
For starters, Linde is very much her own beast, serving as a bit of a faster mage than Robin with huge Magic & Luck. Luck has been established as one of if not the best stats in the entire game thanks to the skills of Luna and Lethality. (I’ve even shown the effectiveness of this) Linde also has huge range and relentless attacks that don’t leave her nearly as open to attack as Robin can in some of his.
Navarre is considered by some to be the best overall character in the game. His statline features more Strength and Luck when compared to Lyn, but less defense, making him a statistically superior version of Lyn with all the same moves besides specials of course.
Minerva may share a moveset with Camilla, but her stats are quite a bit different, sacrificing all of her Magic and some Skill while she has more Luck and Strength. An efficient player should be able to make more effective use of Minerva, though Camilla can sport a unique Topsy-Turvy build, while Minerva performs a more traditional combat role although Camilla is still really good and well rounded along with her musou attacks being overall better with more skill and wider range as well.
Hope you enjoy!