I hugely recommend The Dark Side of the Sun, one of Terry Pratchett’s first books and pure science fiction at its very finest. It’s a story about this very subject and includes all these ideas and more about what “alien” really means. The spectrum goes from a few fairly humanoid species that are really incredibly different in their outlook on life to creatures that would consider those species brothers to creatures that would be incapable of even considering those species “life”. It also takes into account sentient planets and oceans and even galaxies as well as different “levels” of sentience via different complexity of robot. The central theme - what is life and where could it have come from? Simply brilliant.
And on the literature front - was it The Hitchhiker’s Guide to the Galaxy or Red Dwarf that had eight-armed aliens that were unique in the galaxy for having invented the underarm deoderant before the wheel? Amusing but there is still a germaine point there I feel.
pan