If I wanted sign my rights over for my 5 year old daughter, may I choose whom I sign them over to? For example to to her grandmother?

I will answer from personal experience with your situation.

My daughter and I agreed that I would assume cusody of her child.  The arrangement was to have been temporary, until she was able to change jobs and work hours that would allow her to care for her child in a more appropriate way.  Because we lived in different cities, I was not able to provide child care for her.

We live in NC, there was a birth father, but he never saw the child and refused to pay child support, even though there was an agreement as part of their divorce.  In NC, we were allowed to go to a lawyers office, have papers drawn up and signed.  I then had legal custody of the child.

The arrangement eventually progressed to an adoption.  At that time the birth father had to be found and sign over his rights to me.  He also was asked to provide a medical history.  A home study was done, medical examinations were required, etc.  Even though it was an in-family adoption, the paperwork was endless.

If there are other family members with custody rights,i.e. the child's mother, then it is possible that she could challenge your decision even if you have been granted custody.  You MUST consult a family law lawyer in any case.