>"You will be arrested for hurling obscenities at mourners regardless of who the dead person is."
The word hurling in the context of insults or obscenities means vocalizing them in a very audible fashion. The article states that the woman at St Giles was not audibly protesting but rather holding a sign. Given that she was quietly expressing her opinion, tasteful or not, it seems she could have been quietly removed without being arrested.
>"In widely seen photos, a woman holding a sign reading "Abolish monarchy" and "F*** imperialism" was arrested on Sunday at St. Giles' Cathedral in Edinburgh, where the queen's body is to lie at rest until Tuesday.
Further the object of their protest was the institution and neither the mourners or the deceased.
The other two people mentioned in the article who were vocal, were outside on public streets and not in a Church. The article states they were near parade barricades. Again the object of their protest was the institution and it was being done on public streets. Surely you are allowed to express your discontent about an institution on a public street. That's not rocket science.
>"And in London, a woman was led away by four uniformed officers on Monday after holding up a sign reading "Not my king" — which has become a trending hashtag — near Westminster Hall."
Again we have a woman who was holding up a sign on a public street "near Westminster Hall."