I know that the grandchildren's parents are using drugs. I also know that the children are being mentally and physically abused.
Yes, under certain circumstances, it is possible for grandparents to get custody of grandchildren. If you are concerned with the situation that much, you should seek counsel from a local family law attorney.
Advice on this forum is for informational purposes only and should never be mistaken as a substitute for legal advice. If you are in need of legal advice, you should consult local legal counsel.