What's everyone's views on allowing your child to smoke weed. What is the age you find it appropriate or what age would you allow it and why?

I'm struggling here. I have been getting my kids older two siblings on the weekends. They want to spend the summer with me. When I say older they are 12 and 10. They have lived and live a different life than my kids have. They are pretty good kids for the most part. There are some things that I have to address with them when in my care but for the most part having them around is nice. There are some concerns I have for their living environment but I try to make sure at my house their needs are met and they have help with basic needs because they aren't getting that at home. I try to be their child appropriate safe space. With this being said I have learned that they smoke weed. My kids are very sheltered and I want to keep them as innocent and child like as long as I can. I brought up this topic
with their dad, he doesn't know but when I asked him what age does he feel it's appropriate he said basically he rather them smoke weed than pop pills and he rather it come from him because he smokes. He also started drinking and smoking very young. On both sides their dad and mom's side there is a history of alcohol/weed/drugs even with grandparents. Is it my place to talk to the boys about it and should I say something to their parents? I honestly feel like there aren't any boundaries at their mom's house and they are free to come and go as they please as long as they aren't bothering her. Their dad is also lacking in the parenting department so together I feel like these kids don't have a good structure. I try not to judge but I do see a lot of where the problems come from. They have seen and dealt with a lot of things they shouldn't have had to. So anyways. what's y'all's opinions and should I just mind my business as long as they don't do it in my home and around my kids ?