It is important to note that Lee, Kirby, and Ditko were all working for Marvel Comics at the time that they created these characters. Marvel Comics owns the copyrights to these characters, and as such, Lee, Kirby, and Ditko did not have the legal right to steal them.
In addition, there is no evidence to suggest that Lee ever claimed to have created these characters himself. In fact, he has always been very vocal about crediting Kirby and Ditko for their work. In a 1990 interview, Lee said, "Jack Kirby and Steve Ditko were two of the greatest talents I've ever had the pleasure of working with. They were both visionaries, and they created some of the most iconic characters in comic book history."
Overall, there is no evidence to support the claim that Stan Lee stole characters from Jack Kirby and Steve Ditko.