Selling house in brazil

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If you purchased and have been paying taxes in Brazil you need to contact a tax professional as to tax in Brazil on real property income. You would have income on a profit. After sale is competed, the buyer would responsible for tax on the real property. At sale the closing company should withhold the tax and paid in Brazil. but who knows for sure.
This is an interesting question. Have a house in Brazil, someone paying taxes. Real property vs. income tax is a different story as to where you would be taxed.

You don´t have to give any of the proceeds to your children. I´m afraid you´re confusing that to inheritance. Inheritance only happens when the owner dies. In fact
the Codigo Civil prohibits such proceedings called "Pacta Corvinae" literally translated as the "Pacto de Corvos". Look at this Article of the Civil Code in Brazil:

"Art. 426. Não pode ser objeto de contrato a herança de pessoa viva."

robal

You pay the capital gains tax, the difference between what you paid for and what you earned for. 

As for the Children, only if you have any outstanding owed Child Support Payments, whether it is a legitimate marriage or your children are out of the wedlock that the Government Agency may garnish you gains.  And they have to make a claim to be able to collect any money. 

If there are no outstanding claims, and you paid the property taxes plus the Capital Gains Tax, you owe not a penny.