Certainly as a matter of law you cannot slander or libel the dead and I definitely consider them fair game for a forthright discussion.
In the case of these two skeletons, so little is known that they are essentially a natural phenomenon; calling them “lovers” is to me no different from calling a geological structure “the old man of the mountain” or the “tooth of time”. Simply a poetic expression.
I personally believe in that proverb (there may be extremes where it would be okay), and many others do too - or else, it wouldn't have attained its status as one.