You are a "person who has the same home address" to your spouse (and your mother-in-law?), you are a brother-in-law to your wife's brother (the intending/sponsored immigrant), you are a son-in-law to your wife's mother who is the primary sponsor (and a member of the same household as you?). One way or another you qualify to count your income in the mix. It is a trick to figure out if you should be a "joint sponsor" OR a "co-sponsor" to your wife or a "co-sponsor" to your mother-in-law (as a household member). You should seek a professional opinion because your financial obligation varies depending on how you agree to contribute.
8 CFR PART 213a—AFFIDAVITS OF SUPPORT ON BEHALF OF IMMIGRANTS
§ 213a.1 Definitions.
As used in this part, the term:
Household size means the number obtained by adding the number of persons specified in this definition. In calculating household size, no individual shall be counted more than once. If the intending immigrant's spouse or child is a citizen or already holds the status of an alien lawfully admitted for permanent residence, then the sponsor should not include that spouse or child in determining the total household size, unless the intending immigrant's spouse or child is a dependent of the sponsor.
(1) In all cases, the household size includes the sponsor, the sponsor's spouse and all of the sponsor's children, as defined in section 101(b)(1) of the Act (other than a stepchild who meets the requirements of section 101(b)(1)(B) of the Act, if the stepchild does not reside with the sponsor, is not claimed by the sponsor as a dependent for tax purposes, and is not seeking to immigrate based on the stepparent/stepchild relationship), unless these children have reached the age of majority under the law of the place of domicile and the sponsor did not claim them as dependents on the sponsor's Federal income tax return for the most recent tax year. The following persons must also be included in calculating the sponsor's household size: Any other persons (whether related to the sponsor or not) whom the sponsor has claimed as dependents on the sponsor's Federal income tax return for the most recent tax year, even if such persons do not have the same principal residence as the sponsor, plus the number of aliens the sponsor has sponsored under any other Forms I–864 for whom the sponsor's support obligation has not terminated, plus the number of aliens to be sponsored under the current Form I–864, even if such aliens do not or will not have the same principal residence as the sponsor. If a child, as defined in section 101(b)(1) of the Act, or spouse of the principal intending immigrant is an alien who does not currently reside in the United States and who either is not seeking to immigrate at the same time as, or will not seek to immigrate within six months of the principal intending immigrant's immigration, the sponsor may exclude that child or spouse in calculating the sponsor's household size.
(2) If the sponsor chooses to do so, the sponsor may add to the number of persons specified in the first part of this definition the number of relatives (as defined in this section) of the sponsor who have the same principal residence as the sponsor and whose income will be relied on to meet the requirements of section 213A of the Act and this part.
Substitute sponsor means an individual who meets the requirements of section 213A(f)(1)(A), (B), (C), and (E) of the Act and 8 CFR 213a.2(c)(1)(i), who is related to the principal intending immigrant in one of the ways described in section 213A(f)(5)(B) of the Act, and who is willing to sign a Form I–864 in place of the now-deceased person who filed the Form I–130 or Form I–129F that provides the basis for the intending immigrant's ability to seek permanent residence.
INA 213A REQUIREMENTS FOR SPONSOR'S AFFIDAVIT OF SUPPORT
(f) Sponsor Defined.-
(5) NON-PETITIONING CASES- Such term also includes an individual who does not meet the requirement of paragraph (1)(D) but who--
(B) is a spouse, parent, mother-in-law, father-in-law, sibling, child (if at least 18 years of age), son, daughter, son-in-law, daughter-in-law, sister-in-law, brother-in-law, grandparent, or grandchild of a sponsored alien or a legal guardian of a sponsored alien, meets the requirements of paragraph (1) (other than subparagraph (D)), and executes an affidavit of support with respect to such alien in a case in which--
