I-864 is not needed for either of you because you are immigrating in an employment-based category (derivative beneficiaries have the same category as the principal beneficiary), as long as the petitioning company is not 5% or more owned by your relative. Both of you would need to file I-944, the public charge questionnaire. Employment-based immigrants are not exempt from the public charge ground of inadmissibility.

In I-485 instructions, the section "Public Charge: Declaration of Self-Sufficiency (Form I-944) and Affidavit of Support Under Section 213A of the INA (Form I-864)" (on page 12-15) lists which categories need to file I-864 or I-944 or both or neither:

Who Must Submit Form I-944 (and not Form I-864)

If you are a principal or derivative applicant, you must submit Form I-944 with your Form I-485 if you are applying under one of the following immigrant categories:

[...]

B. Alien worker under the employment-based preference categories (Exception: You may also need to file Form I-864 if a relative filed Form I-140 for you or has five percent or more ownership interest in the business that filed Form I-140 for you. See the list above for more details.);

On both of your I-485 forms you would check "No" in I-485, Part 8, item 61, "Are you exempt from the public charge ground of inadmissibility?". And then both of you would check the box in Part 8, item 62d,

I am EXEMPT from filing Form I-864 because:

62.d. I am applying under an alien worker (Form I-140) employment-based preference immigrant category and both of the following apply:

(1) I am not a relative of the Form I-140 petitioner; and

(2) I do not have a relative with a significant ownership interest (at least five percent) in the business that filed Form I-140.

USCIS Policy Manual, Volume 8, Part G, Chapter 13 appendices also contains tables for whether each type of Adjustment of Status applicant needs to file I-864 and/or I-944.

I-864 is not needed for either of you because you are immigrating in an employment-based category (derivative beneficiaries have the same category as the principal beneficiary), as long as the petitioning company is not 5% or more owned by your relative. Both of you would need to file I-944, the public charge questionnaire. Employment-based immigrants are not exempt from the public charge ground of inadmissibility.

Update: As of March 9, 2021, the public charge rule has been vacated. Neither of you should file I-944 with your I-485. See the alert at the top of the I-485 page.

In I-485 instructions, the section "Public Charge: Declaration of Self-Sufficiency (Form I-944) and Affidavit of Support Under Section 213A of the INA (Form I-864)" (on page 12-15) lists which categories need to file I-864 or I-944 or both or neither:

Who Must Submit Form I-944 (and not Form I-864)

If you are a principal or derivative applicant, you must submit Form I-944 with your Form I-485 if you are applying under one of the following immigrant categories:

[...]

B. Alien worker under the employment-based preference categories (Exception: You may also need to file Form I-864 if a relative filed Form I-140 for you or has five percent or more ownership interest in the business that filed Form I-140 for you. See the list above for more details.);

On both of your I-485 forms you would check "No" in I-485, Part 8, item 61, "Are you exempt from the public charge ground of inadmissibility?". And then both of you would check the box in Part 8, item 62d,

I am EXEMPT from filing Form I-864 because:

62.d. I am applying under an alien worker (Form I-140) employment-based preference immigrant category and both of the following apply:

(1) I am not a relative of the Form I-140 petitioner; and

(2) I do not have a relative with a significant ownership interest (at least five percent) in the business that filed Form I-140.