Have fun in A'dam Fuji and stay out of the Regulierdwarsstraat (unless going for cocktails at door 74). PM me if u want any specific tips for places to go.
As far as morality goes, 4th person sure, but last resort. Had similar dilemma once and we got 4th person on days notice for 150 quid which seemed fair. gain/loss @50% divided equally.
only reading hendrix's post now. he beat me to it.