My BIL is in his mid 30s and has had substance issues for a while on and off (a decade or so). Two years ago he landed in the hospital with an unrelated issue that his substance use had made worse. He lived with his parents for a year and 6 months ago got his own place.
He has a job doing landscaping for the summer and his coworker (who used to mow our yard through the company) rang our doorbell and said he's so worried about BIL regarding substance use while driving again but doesn't want to tell BILs parents as they would freak out. My husband thanked him and passed the message along to his parents.
The next time he was visiting his/ my husband's parents, they checked his car and all looked ok and he said that the coworker was just trying to make trouble for him. This doesn't make much sense as he would have made an anonymous report to his employer if he really wanted to make trouble?
In any case my in laws have let it go and it seems like there's not too much more to be done. Am I unreasonable for still being concerned he may be drinking and driving/using stronger substances?