What rights are you talking about? Are they parents? To give the 19yo custody or terminate the 15yo parental rights you have to go to court to do so. The 19yo have to petition for custody.
His decision to sign over his rights has to be approved by the courts.
No, as the parent no longer has jurisdiction over the child.
As a parent you always have that choice even if you are 16 or any other age.
None.
no
You can, BUT they either have to be wards of the state or their parents/legal gaurdians sign over parental rights to you. If not, you could be charged with kidnapping or harboring a runaway. If the parents don't care the child is missing, they will most likely sign away their rights.
No, it's not legal, but a parent can very well sign over their parental rights to you at ANY time & put you in the foster care system.
Everything period
The same rights they had when they were younger. Your child is not 18 yet.
No they can not.
No: usually you must be over 18.
No. A thirteen year old cannot execute a "legal" document.