If you want finished quest "Investigate the Suspicious Toys" this is simple. You don't lose reputation and don't climb on roof.
Fisrt step: yuour team must outside firework shop - far! Maybe next to teleportation portal.
Second step: you must summon "fire elemental" (max 3 or more spells or scrolls) and send him (only him!) to last floor in firework shop. First NPC reaction is panic and next step fight with fire elemental. Use fire attack on all barrel with powder and kill NPC (use normal attack on NPC when barrels gone). When fire elemental is gone send new elemental.
All fight must take place on secend and last floor.
My advice: kill all NPC in the shop except to costumers in first floor: kid with white hair, dwarf and "Flaming fist" outside the shop** (this people are innocent). Other people in shop always working for Gortash.
** "Flaming fist" outside the shop sometimes join to fight. Don't attack this "Flaming fist"! Avoid combat with him.
Third step: send away fire elemental when kill everybody working for Gortash (remember: except to costumers).
Quest done if you kill them all.
Your team is cleare reputation and beyond suspicion.
(Note. If you send your team in last floor you hear always "do not enter".)
