The process for finding out is a child can be taken as a dependent is to run both possible tests (qualifying child & qualifying relative) "against," so to speak, every situation (your parents, you, your brother, the father, etc)
For the child tax credit, can be partially refundable, here's the basic test:
To qualify for the Child Tax Credit, you must have a child or dependent who meets all of the following requirements:
The child must have been 16 or younger on December 31.
The child must be a United States citizen, a United States national, or a resident alien.
The child must be claimed as a dependent on your tax return.
The child must be related to you in one of the following ways: son, daughter, stepson, stepdaughter, brother, sister, stepbrother, stepsister, grandchild, niece, or nephew. This includes any legally adopted child, any child lawfully placed with you in preparation for adoption, and any foster child lawfully placed in your care.
The child must have lived with you for more than half of the year (stayed with you for at least 183 nights). Temporary absences for special circumstances are generally acceptable, and special rules may apply if you are divorced or for certain other circumstances. For more details, please see Publication 972, Child Tax Credit.
The child must NOT have provided more than half of his or her own financial support for the year.