Call a lawyer, many of them do free consult's. Just keep in mind though that if you take these kids away from her she might hate you forever, so weigh in on what's more important. So sorry your dealing with decision's like these!

You as a grandparent if you cannot get your daughter to seek professional help, you need to report the abuse to the cps inorder to get the cps involved to help the mother and the children, the cps can open a child abuse case and grant you guardianship of the children until the case has been resolved, meaning if the cps files any charges against the mother for abuse they can make the mother seel help inorder for her to get the children back, if she refuses then she will not get custody back. The cps can make the decition to place the children with you and usally prefere to do so instead of placing them in foster care. If the doctor notices marks of abuse it is their oblagation to report it to the cps, they have to do this they cannot just do it because you state it to them they need some form of evidence. You may want to talk to your daughter and see if she will consent allowing you to file for guardianship, this is the best way to go if she will agree. The cps can also give the mother a choice on allowing you to file for guardianship instead of removing the children or opeing a case. You can also consult with a lawyer and try to file for guardianship if you have evidence that the children are being abused, pictures of marks, doctor statements ect would work even any wittness you may have that has seen the mother abuse the children like neighbors, as for the mother abusing or harassing the neighbors they can file a report and get a restraining orser against her.