What would you do if you thought your kids were drinking

I have 3 kids, 16, 13, and 11. It's my 16 year old who I've had suspicions has been drinking. They lost their dad a year ago and the relationship I had with their dad was toxic. He was an alcoholic and while never physically abusive, we fought a lot. I stayed with him because I'm not a believer in divorce and wanted to fight for my marriage and thought my kids would do better in a two parent home. He ended up drinking himself to death. He wasn't a bad person. He had a lot of demons and used alcohol to cope. We separated for a short period 3 years ago. My oldest was in the 7th grade and my husband picked him up from robotics club. He was drunk and got into a car accident with our son and our son's friend in the car. It was horrible. We separated for 2 months and got back together because I wanted to keep the family together. I know this is a lot of back story but point is they've been around a lot of alcoholism and losing their dad was hard. The reason I think he's been drinking is because when he's come home he darts straight for him room and I notice him walking funny. I'll try to have a conversation and he won't really reciprocate the conversation and when he does he slurs his words which is why I think he's been trying to say as little as possible. We had a problem with him lying to me about staying with his cousins for the weekend and he actually went with his friends to God knows where so he got grounded. I haven't approached this because I don't know how. He obviously won't be honest with me if he is drinking. I feel defeated that he may be falling into his dad's food steps. I didn't know what to do about my husband. Idk what to do about my own child.