My parents did an estimate on their taxes and they claimed my 3 siblings, the estimate was less than last year. I am 21years old still live with my parents, and I am a full time student, I have helped my parents buy clothes for my siblings also buying groceries. Can I claim one of my siblings as a dependent.
Yes and no.
A child can be a qualifying child dependent for any relative in the household. But, there is an additional rule:
If the parents of a child can claim the child as a qualifying child but no parent so claims the child, no one else can claim the child as a qualifying child unless that person's adjusted gross income (AGI) is higher than the highest AGI of any of the child's parents who can claim the child.
So, unless your income is higher than your parent's, you can't claim your siblings.