Let me be frank with you - during divorces, property distribution
, and custody issues - people lie, cheat, and steal. The court is very aware of this and sees it all the time.
As such, the court isn't going to demand something as intrusive as a drug test on the basis of an "ex" spouse who has an "ax to grind" and where some ex spouses would do anything and everything in their power to cause grief to the ex, not pay them, obtain custody, and see them completely humiliated, etc..
So, what you can and should do is immediately deny her custody of the children based upon your "smelling" of drugs - in fact, it would be parental negligence of you to allow her to take the children if she's been doing drugs (illegal or otherwise).
So inform her that your not going to allow her to take the children and call the police - let them take it from there AND if she's even charged - then you can immediately petition the court for sole and primary custody and termination of your child support (in fact she would be obligated to pay you child support).