I don't see how extending the shorter 50/50 arrangement to a slightly longer 50/50 arrangement is going to help at all. If the mom found it then she needs to address the situation in her home. Did she back up your DH when he found the cigarettes or vice versa? Did your DH back up BM back when she found the cigarettes? If pot is illegal in your state then perhaps both of his parents can take him to the local jail and have an officer speak with him about the penalties of getting caught with it. If it's legal but parent don't approve then perhaps they can bring him to a place that educates children's the dangers of being under the influence such as drugs & alcohol while driving, show him the costs of having a habit like smoking weed and/or drinking and where most of those people end up. Education and consistency is their best bet...he's a teen so he's going to be tempted.

If think the key question is who is he trying to impress? Are they a good influence?

I can see the advantage in one custody change per week vs 3/4....

Someone else's SD (I think) was smoking tea leaves! lol My SS17 could hook him up with the real stuff if he wanted, cause he's pretty fly for a white guy!