Summary: The player is tasked by Great House Indoril to find Madril Berend and convince him to join House Indoril. This quest is tied to http://tamriel-rebuilt.org/claims/brother-against-brother
The claimant is encouraged to get creative with this one. A most basic outline is the player 1) finds Madril 2) Does something to convince him to join House Indoril 3) reports their success or lack of it to the quest-giver, finishing with an optional 4) seeing Madril through his initiation ceremony to House Indoril.
This quest wouldn’t be tied directly to Brother Against Brother, but dialogue would need to be sensitive to what happened in that quest. AKA, the player may be required to convince the grieving Madril to join Indoril after he killed his brother, may need to find the two brothers after their pilgrimmage is completed (most likely in Saint Aralor’s monastary, see UESP map link), may get offered the Brother Against Brother quest because it’s the first time they’ve met Madril, etc, etc.