Yeah, godparents don't tend to get custody. If the parents want the godparents to have custody if something happens to them there are a number of other legal steps that they'd have to jump through to make the happen. It isn't unheard of for non-family members to be able to obtain custody but there are hoops that have to be jumped through that can make or difficult.

Also, there are a number of things involved with this. If she has weed in her system the hospital would have to be aware of it and not all hospitals do drug tests after the child is born etc. Also, a lot of the time, they will do a test on the baby to determine if it has drugs in their system. There are people who end up not losing custody of their child when they have Marijuana in their system after the baby is born because the baby ends up not having it in their system. So, there are plenty of factors involved and different states and cities handle it all differently.

In regards to the rest, your friend has to be willing to seek help for his delusions. You can talk to him but if he isn't willing to get help there really isn't much that can be done unless his delusions end up endangering the life of the child. At that point you could contact CPS but it's up in the air in regards to of they will do much etc.

I also don't know how common it is for a baby to not have it in their system since I don't know too many people who continued smoking it once they found out they were pregnant.