Second passport

Maryam,

Your Brazilian-born child will have Brazilian citizenship from birth.  Brazil does not issue second passports, or passports of convenience.  The only way for you and your husband to obtain Brazilian passports is to become naturalized as Brazilian citizens.
To do that, you both will have to apply for permanent residency when your child is born.  After permanent residency is granted, and after you live in Brazil for a year, counting from the date that your permanent residency is approved,  you can apply to become a citizen.  The normal residence period is four years, but it's shortened for the parents or spouses of Brazilians.  After your citizenship application is accepted, it can take another year for it to be acted on, during which time you're expected to be living in Brazil.  Only after your naturalization is approved can you apply for a passport.  There are no shortcuts.

Abthree
Thank you very much for your answer, but what if we buy a house? wouldn't this help to get our residency or passport faster?!

No.  Buying real estate will not have any impact, either positive or negative, on your application for permanent residency, or any eventual application for naturalization.  It would, however, introduce significant additional complications and stresses into your lives, while you're preparing for and then recovering from the birth of your child.  You should definitely check out the comment threads here on buying a home before you commit to that course.