AMCAS disadvantaged status means economically disadvantaged, medically underserved area, or immediate family (defined by AMCAS).
Disadvantaged Status
Ultimately though, your perceived status is up to you. You decide if you check the box "disadvantaged" on your application, or not. Maybe your circumstance doesn't neatly fall into one of the three categories. Either way, if you select yes, then you are prompted to write an essay for the purpose of describing your situation (AMCAS).
After that, each school looks at your status in a different way, as each school has its own policy on how to take your essay answer into account (google).
Maybe they would count something in your favor that isn't listed in AMCAS (speculation).
That's absolutely awesome that you took care of your family member. Maybe if it was important to you, you can share that as part of your story in future essays, regardless of your perceived status.
Everyone needs good grades and MCAT scores though, so focus yourself there (common sense).
(Sources: google, amcas, speculation, common sense)