The LN only tackle the negotiations with Roper forces and him accepting the negotiations. No mini arc of rescuing Roper pregnant wife.
The Battle in Rolts:
- without Roper's wife plot, the motivation for Roper betrayal was for his career advancement since he also have high Political traits.
- Dan Allest is beheaded by Reitz during the ambush in the forest.
- Count Jean/John Tendry is also slain during this battle.
Dan Allest and John/Jean Tendry is not mentioned as brothers in the LN.
So it's most likely we will not see the Allest brothers in the future manga story.
Even though the manga have expanded on this Rolts story. It show a more character development than in LN. Which I favor more than LN.