If it is proved that the grandmother's house is an unsafe environment, go ahead and remove the boy and mother. But profanity is not adequate basis for judging a home as unsuitable.
I agree with you and also think that the boy and his mother should be kept together if possible. One thing here is that people do such idiotic things with children. In my lifetime I've see a father pick up his son, a boy about this age, then carry that boy to his mother as he tells the boy what to say to her.
The father takes the boys arm and strikes at the mother saying "just call her an old bitch", or "tell her she's this and that," etc. None of this is "funny" or any way to teach or treat children. None of it is "cute" and it's damned near criminal. The example I'm giving here did not come out of a Thug Circle or gang environment.
that's nuts wow!