Becoming the legal guardian of a sibling is never an easy task. In addition to being stressful emotionally and possibly financially, legality is often an issue. Guardianship of a minor or vulnerable adult can be granted to siblings, but the process may involve more work than gaining custody of one's child.
Familiarise yourself with the guardianship laws of your state. Different states have different laws regarding who can become a legal guardian to whom, and it will be in your best interest to learn how your state's laws apply to you if you wish to move forward with becoming the guardian of a sibling. This is especially true with gaining guardianship of a legal adult. You may perform the research yourself or you can enlist the expertise of a lawyer to learn how guardianship is handled in your state.
Speak to your sibling's legal guardians and ask them if they would be willing to relinquish custody. If they do not believe that they can provide adequate care to your sibling, they may be willing to discuss this matter and come to an agreement that satisfies everyone involved. This will obviously make the process much smoother. In cases like this, it never hurts to attempt the simplest solution first.
File a custody application in the state or local court where you and your sibling reside. Most of the time you will have to file in the state court, but if your sibling already is living with you, the local courts may suffice. This depends on the laws of your state, so make sure you do plenty of research to know what those laws are. Alternately, you may also speak to the clerk at your local courthouse to answer some of the questions you may have about jurisdiction.
Demonstrate in a court of law that you are capable of becoming the guardian to your sibling. This can be difficult, as siblings tend to be close in age and one cannot become the guardian of a legal adult unless said adult is unable to make decisions effectively on his or her own. Generally, the process of becoming a guardian will involve proving that your sibling is in a situation where he or she is unsafe. This can be in cases of neglect, abuse or otherwise being in an environment that is harmful to your sibling. You must also prove that you are capable of providing the necessary care as well.