No, unless your mother in law lists her as a dependent. You are in your wife's household as well. If you have a joint sponsor, your wife's income doesn't really matter. But she still needs to prepare an affidavit of support.
I usually look around the breakfast table and count heads. I will transfer you into the Immigration Section in case they have a more exact method.
We offer general concepts, but you should give ALL your facts to a licensed Attorney in your state before you RELY upon any legal advice.
The form itself tells you who gets counted.
J Charles Ferrari Eng & Nishimura 213.622.2255 The statement above is general in nature and does not constitute legal advice, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship. Answers on Avvo can only be general ones, as specific answers would require knowledge of all the facts. As such, they may or may not apply to the question.