1. You need to send a copy of the original birth certificate and a certified translation of it (no need to notarize it). You can find the following information at:
http://uscis.gov/graphics/fieldoffices/scnational/index.htm#H
Please submit certified translations for all foreign language documents. The translator must certify that s/he is competent to translate and that the translation is accurate.
The certification format should include the certifier's name, signature, address, and date of certification. A suggested format is:
Certification by Translator
I typed name , certify that I am fluent (conversant) in the English and languages, and that the above/attached document is an accurate translation of the document attached entitled .
Signature
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Typed Name
Date
Address
2. Non-immigrant visa number is the control number.
3. Yes, it is sufficient to have a joint sponsor.
"If the visa petitioner's household income is not sufficient to meet the requirements of INA section 213A and 8 C.F.R. § 213a, INA section 213A permits a joint sponsor to sign an affidavit of support, in addition to the affidavit of support signed by the visa petitioner. A joint sponsor is someone who is willing to accept legal responsibility for supporting your family member with you. A joint sponsor must meet all the same requirements as you, except the joint sponsor does not need to be related to the immigrant. The joint sponsor (or the joint sponsor and his or her household) must reach the 125 percent income requirement alone. You cannot combine your income with that of a joint sponsor to meet the income requirement."
Read more about it on this page:
http://uscis.gov/graphics/howdoi/affsupp.htm#sponsor