my mom, dad, brother and i came to the us in 1980, we were all isssued
permanent residence cards, my parents became citizens in 1992, i was
12 at the time, did i also obtain my citizenship at the time and is
there any documentation i can get to prove that?

Hi preachersao,

Yes, from what you've said, you automatically acquired U.S.
citizenship when your parents became citizens and you can apply for a
Certificate of Citizenship at any time. After you obtain the
certificate, you'll be able to use it as proof of citizenship to apply
for a passport.

Instructions for Form N-600
"If you are the biological or adopted child of a U.S. citizen, you
were born outside the United States and you are claiming citizenship
by action of law, you automatically become a U.S. citizen if:
* You have at least one parent who is a U.S. citizen, whether by birth
or naturalization; and
* You regularly reside in the United States in the legal and physical
custody of your U.S. citizen parent; and
* You have been lawfully admitted for permanent residence
* You have not yet reached your 18th birthday; and
* You are a biological child, you were legitimate 
NOTE: If you are now over the age of 18 years but all of the above
conditions applied to you before your 18th birthday and you were under
the age of 18 on February 27, 2001 (the date the law took effect), you
may file this form to obtain a certificate of citizenship."
http://www.uscis.gov/graphics/formsfee/forms/files/N-600.pdf

N-600, Application for Certificate of Citizenship 
http://www.uscis.gov/Graphics/Formsfee/Forms/n-600.htm

How to Apply in Person for a Passport
http://travel.state.gov/passport/get/first/first_830.html

I was glad to find this for you. If you have any questions, please
post a clarification request and wait for me to respond before
closing/rating my answer.

Thank you,
hummer

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