Well, you can choose to have a shared pool of money or keep separate "wallets", there's a book in the mayor's house that will let you toggle between these options. Another good thing to know is that the elevator in the mines works for everyone, so if you make it to level 40, everyone else can use the elevator to go right to level 40. Also a lot of things are player specific, each player can collect rewards from chests in the mines, from the museum, and all quests are per player, so each person will need to do each step of quests.