AMCAS doesn't automatically designate you as disadvantaged based on family income. The family income field could be used individually by schools to categorize their applicants, however this will vary from school to school.
You can be automatically classified as socioeconomically (SES) disadvantaged (EO-1 or EO-2) based on your parents' occupations and highest educational levels. See the AMCAS applicant guide for more details.
You can also classify yourself as disadvantaged, for economic/education/cultural reasons etc. You will have to explain your choice in a paragraph. $25k to $50k per year is quite low for a family of two or three. However, if you want to use that as a reason for marking yourself as disadvantaged, you will probably have to go into more detail about how your family's low income placed you at a disadvantage compared to other students.