My daughter lives in Florida she is 21 has two kids and one on the way. We have discuss taking guardianship over her oldest child. What is it that we have to do to make this happen

Get an attorney to draw up a guardianship agreement and have it ratified by a local Family Court.

Agreed, the court may want to know about the status of the bio father also, but an motion is drawn up and filed in famiily court, there will be a hearing ( or several ) with the judge and a ruling is made.