If you are a noob quests are a challenge. But you may be a persistent SOB type of noob, so here we go.
Where is merchant's brother spawned? Here's how to go about it:
1. The merchant brother must be a separate troop, so first search the troops file for "brother" or whatever his onscreen name is.
You get this:
["relative_of_merchant", "Merchant's Brother", "{!}Prominent",tf_hero,0,0,fac_kingdom_2,
[itm_linen_tunic,itm_nomad_boots],
def_attrib|level(1),wp_melee(10),knows_athletics_1|knows_ironflesh_2|knows_shield_2, 0x00000000320410022d2595495491afa400000000001d9ae30000000000000000, mercenary_face_2],
2. Now if you search the module system for "trp_relative_of_merchant", you will get all the references for the brother, including his spawning code. Like here in the "bandit_lair" mission template:
...
This sequence:
(try_begin),
(eq, ":starting_town_faction", "fac_kingdom_1"),
(assign, ":troop_of_merchant", "trp_relative_of_merchant"),
... is followed by code to find the nearest entry point, and spawning the brother there:
(add_visitors_to_current_scene, ":nearest_entry_point", ":troop_of_merchant", 1, 0),