I'm confused about the 'Additional Family Information Form IMMM 5406'. I am the applicant and am married to a Canadian citizen who resides in Canada. Neither of us have any children. Do I (applicant) still fill out Section A and put my spouse on the 2nd line even though he is a Canadian?
Yes, you have to put your spouse on line 2. If no spouse is listed, you have to sign below that section certifying that you have no spouse, meaning any spouse, including a Canadian , has to be listed.
Do I also put my parents who are Americans and are not immigrating anywhere?
Yes, list your parents in the first section as well. The parents don't submit medicals or photos, but they do have to be listed here.
Also, Section C says brothers and sisters, do I have each of my brothers fill out one of these forms as they are not immigrating anywhere either?
You have to fill out Section C, listing all your brothers and sisters, including half-and step-siblings. But they do not have to submit photos or medicals, as they are not immigrating.