Who Can I rightfully claim as Dependent?

you can claim a "qualifying child" or "qualifying relative" if they meet requirements related to residence, relationship, age, financial support, and income. Even significant others or friends can qualify in some cases. According to the IRS, a “qualifying relative” can include an unrelated person who passes the four tests below. You cannot generally claim a married person as a dependent if they file a joint return with their spouse.

• Relationship: Must be your child, adopted child, foster-child, brother or sister, or a descendant of one of these.
• Residence: Must have the same residence for more than half the year.
• Age: Must be under age 19 or under 24 and a full-time student for at least 5 months. They can be any age if they are totally and permanently disabled.
• Support: Must not have provided more than half of their own support during the year.
• Joint Support: The child cannot file a joint return for the year.

There are 4 tests that will qualify a relative as a dependent as follows

• They are not the “qualifying child” of another taxpayer or your “qualifying child.
• Gross Income: The person cannot have a gross yearly income over the limit.
• Total Support: You provide more than half of the total support for the year.
• Member of Household or Relationship: The person must live with you all year as a member of your household or be one of the relatives that doesn’t have to live with you (Your child, grandchild, or great-grandchild, your legally adopted dependent, your stepchild, stepbrother, stepsister, your brother, sister, half-brother, or half-sister, your parent, or other direct ancestor, but not a foster parent, your stepfather or stepmother, your parent's brother or sister, your brother's or sister's child, your mother-in-law, father-in-law, brother-in-law, sister-in-law, son-in-law, or daughter-in-law.

Resource

• Who Can I Claim as a Dependent? Dependent Taxpayer Test