I don't think that I-864 is needed. Employment Letter is require

Please read the following paragraph regarding "Affidavit of Support" in the Instructions of the official I-485 form:

-- Affidavit of Support
an Addidavit of Support (Form I-864) if your adjustment of status application is based on your entry as a fiance(e), a relative visa petition (Form I-130) filed by your relative, or an employment based visa petition (Form I-140) related to a business that is five percent or more owned by your family.