What happens to all my assets outside US if I die?

First question: Do I need to register this house in my tax return here in US?

There is no "registration" of foreign property (whether real estate or stocks or anything else) on a US tax return, but, as a permanent immigrant, your world-wide income is subject to US tax, and so I hope that you have been declaring the income generated by these foreign properties (e.g. rental income, dividends, interest, etc) on your US tax returns all these years. If not, I recommend that you file amended returns.

Second question: Suppose the scenario that I don't have a will and I die... what happens to my house in Brazil?

This is more of a legal question than a financial one, and is better asked over on Law.SE. Someone will need to settle your estate in the US, too , and you better be prepared to reveal whether you have any dependents in Brazil or in the US in order to get more useful answers.