You are right to be concerned. As you are probably aware, addiction to pain medications is very difficult to treat. The person is usually obtaining their drug of choice legally and it is supported by their physician. What you are describing certainly sounds like an addiction problem. Unfortunately, there is not much you can do. Keeping your distance is smart and the healthiest thing you can do for yourself. It is likely that they will have a crisis at some point, be ready, they will be most open to help and intervention at that time. In the meantime, distance yourself, detach from their issues, but be loving and supportive. They will react negatively to your efforts to intervene but they will feel your love. Find support for yourself, this is not going to be an easy situation.
I have been to Alanon in the past to help deal with my now deceased ex husband's drug and alcohol problems. I have all the meditation and daily thought books. Really like Melody Beattie.
There are many prescribing doctors as my daughter-in -law shops around. I have not been to their home in several months. A few times I went over and was not allowed in.
I have a friend who lost a son to heart failure from drug abuse. HIs other son was an abuser in his 20's Now he is in his mid 30's and experiencing heart problems, potentially fatal, as well from his past drug use. Young people don't realize how their drug use can have detrimental effects later on. This is what worries me as well.