Well one obvious sign that the wealth of the Dedalus' family;s decline is the fact that their furniture gets repossessed, another is the fact that the Dedalus family has to sell their properties. At the beginning of the chapter, Stephen knows that something is wrong, but he doesn't really understand why. By the chapter's end, Stephen realizes that his family is in serious debt.
With Stephen's winnings, he takes his family out to a lavish dinner, telling them to order whatever they want, buys gifts, and takes people to the theatre. He is uncautious with his money, a spendthrift. He clearly likes luxury and pleasure.