Does USCIS accept co-sponsors / joint sponsors on Adjustment of Status from K1 Visa applications?

Yes they accept co-sponsors for Adjustment of Status / AOS from a K1 Visa and it doesn’t matter if they’re blood-related to you or not but they must be :

• Be U.S. citizen or national or a permanent resident
• Be at least 18 years of age
• Be domiciled (live) in the United States
• Meet all of the financial requirements of a sponsor pursuant to INA 213A

As defined by USCIS:

“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% income requirement alone. You cannot combine your income with that of a joint sponsor to meet the income requirement.”

–
Affidavit of Support
USCIS.gov

Some things you need to remember:

• I-864 is a legally-binding document.
• Same requirements with Primary Sponsors apply to Joint Sponsors.
• Needless to say, it’s the same duties, responsibilities and obligations too.

If you’re asking someone to be your joint sponsor, it’s only fair to let them know what being a Joint Sponsor entails. Show them the links below:

• What are my duties and responsibilities as a Sponsor signing the Form I-864?
• When will my obligations as a Sponsor on I-864, Affidavit of Support end?

If you’re looking for co-sponsorship / joint-sponsorship for the K1 Visa Interview in U.S. Embassy Manila: 

• Does the U.S. Embassy in Manila, Philippines accept co-sponsors / joint sponsors for a K1 Visa Application?

Sources:

• USCIS.gov – Affidavit of Support