Disabled
An exception to the rule that parents' duty to support their children ends at the children's majority occurs when the child is disabled. In cases where the child is disabled, mentally or physically, and therefore unable to support himself/herself upon reaching the age of majority most states have adopted the rule that parents have a duty to support their adult disabled children. Most often, courts define "disability" in economic terms, i.e., the inability of the adult disabled child to adequately care for himself/herself by earning a living by reason of mental or physical infirmity. States differ as to whether support for an adult disabled child is determined by the state's child support guidelines or by the needs of the child as balanced by the parents' ability to provide support. In the case the child CAN support themselves then they'd be legally an adult at their states normal age of majority which is generally 18.
Yes
It can happen.
When the child is emancipated or has attained the age of majority (support may continue for an adult child who is severely disabled); when the child has been adopted; when the parents are married to each other and living with the child.
Is there a grant for a single mother with a disabled adult to buy a car for transportation for his needs or to pay bills.
Neither has more right then the other, they are equal in the minds of the law.
No you cannot be adopted because you are already over 18 years of age. you are a legal adult
Any types of adoptions or parental rights sign offs have to be done in front of the courts. The adopted child could be signed over to another adult as long as that adult is found to be fit enough to be capable of the upbringing of the said adopted child.
Forever
If the adult brother doesn't have legal custody of the adult sister (if she were severely disabled, severely retarded, etc.) then he's not legally responsible.
no