I am asking friends and family to fill out affidavits as required by the Immigration form I-130 to provide testimony attesting to my marriage and relationship with my wife (non US citizen). Would it be necessary for my friends to include their social security numbers in their affidavits?
No. But do submit proof of their identify and immigration status.
The above is intended only as general information, and does not constitute legal advice. You must speak with an attorney to discuss your individual case.
Typically affidavits of friends and family are given relatively little weight, and are usually used in cases where there is reason to suspect marriage fraud. Other evidence of the good faith nature of the marriage is going to be more important.