I would use A. But I wouldn’t go so far as to say that B is incorrect. It sounds odd and old-fashioned to me, but there are examples of "have been long known as" in published books. You can confirm that if you do a google search with "have been long known as". Here is an example from a chemistry journal: (https://www.princeton.edu/chemistry/macmillan/publications/Tracy_Orgcat.pdf) "Oxy-allyl cations have been long known as transient electrophilic species since they were first employed as intermediates in the Favorskii rearrangement in 1894."

A is correct. A. These creatures have long been known as our friends.