In your original sentence, you are trying to use "them" as an adjective to modify "incompetent developers," but "them" should only be used as a 3rd person plural pronoun. Using "them" as an adjective is not proper; your examples sound strange to native speakers, and is usually associated with vernacular English in general. Native speakers may assume this usage is due to poor knowledge of proper English, or possibly a regional (improper, but common) usage in the American South.
https://grammarstars.blogspot.com/2008/08/41-them-and-those-...