SpoilerTo make sure that it is clear for everyone. The promisary note of 2,000GP is for the group, not per person although if you are successful in solving the riddle, you can try to convince Tunaster to add an extra 500GP to pay for the 5th share.
SpoilerLet me know if you want to see what rumors you can get from the town people first or go directly to the temple and what approach you will take for your visual inspection of the property.