will it be hard to get custody of our grandchildren

we have had two of our granddaughter since she was about 5 years old she is 16 now and we have had her brother since he was 3 years old he is going on 10 the mom to them is our daughter she has been on drugs every since High School. she has been in and out of jail. But now she is in jail for introduction awaiting her court date. We need to show custody papers on both and that is something we don't have We did not want to prove our daughter unfit but it is time we did something about this situation but don't know where and how to start