We need to know what information we need to try to get custody of our grandchildren

The question is whether you have standing to pursue a third-party custody action. As a general rule, the law recognizes the right of parents to raise children, without undue interference from the state or other parties.  However, there are exceptions and you must prove by clear and convincing evidence that it is in the best interest of the children for a court to intervene.  These cases are very difficult to win because of the Constitutional issues involving a parent's right to autonomy when raising children.  There are two ways to handle this situation.  First, it would probably work best for you to reach an agreement with the parents granting you temporary custody.  If they are unwilling to reach an agreement, then, you have to go to the local Juvenile and Domestic Relations Court and file a Petition, seeking custody.  If both parents oppose your request, then, you have to prove actual harm to the children by leaving them with their parents.  If only one parent disagrees, then, you have to prove by clear and convincing evidence ("CCE") that it is in the best interest of the children to be placed in your custody. Unfortunately, the CCE standard is rather high and will require definitive proof of any allegation.  You can't rely on hearsay evidence but you must be able to convince the court, based upon your personal knowledge that the parents pose a danger to the children or are unfit to serve as caregivers. I suggest that you set up a consultation with an experienced family lawyer in your area.  Lawyers charge by the hour for consults, so you need to discuss the cost of a consultation in advance to avoid any issues.   Best of luck~