I never heard of soul twins before but it completely describes me & my lover. I feel like we're the opposite sex versions of each other. Besides all our similar interests & personality traits, we even have similar physical complaints. He is not a spiritual person so I'm not even going to mention this to him. I'm interested to see how it all unfolds though.
I do not ascribe to any dogma but consider myself a very spiritual person. I deplore most organized religion particularly if it believes in sin or is not based on the concepts & practice of love & compassion. I am also a very scientific person believing that almost anything is possible (not something like Creationism though) & am open to infinite possibilities. When one gets into the study of quantum physics & mechanics, the possibilities of such things as the origins of our universe, the existence of sub-atomic particles (e.g. God Particle/Higgs-Boson), and the space/time continuum are mind-blowing. I believe that we probably experience many lives and reunite with other past lives & this is probably the origin of the twin souls. One could balk at the concept of past lives but it can probably be explained in terms of science one day. I cannot say that anything is for certain, nor can I refute certain possibilities that I may not understand. I don't think that being Agnostic means you must deny the existence of such a concept as twin souls. To me being agnostic means that you openly admit to not having the answers and choosing to not accept false answers when confused about a particular aspect of spirituality or the unexplainable.