How do I explain to reform jews and the even less observant forms than reform, why reform, conservative, and all the less observant types, are not the real torah?

Shalom, Thank you for your question. Before answering let me make the following point – very few people are ever convinced by arguments (no matter how good those arguments are), in changing their belief system. All the more so when they are having someone else explain to them why what they believe in is wrong. It is usually unsuccessful to try and prove or explain to someone what they are not living “the real torah”. Rather, an approach that sees the less observant jews as people who are able to (perhaps slowly) grow to take on more in their Judaism is more successful. Rather than explain why they are wrong – let them feel good about the good things they do, and add to that more and more involvement. For example, one does not have to get involved in arguments about why mixed seating in synagogue is not correct. Rather, be positive that they are going to synagogue at all. “You go every Friday night to the Reform shule! That’s great – maybe you’d like to join us at our shule on Shabbat morning too. We have a great kiddush after shule. Can I invite you for lunch?” (you get the idea). [Let me point out, that this is not a mere strategy, but a very real belief and love for every Jew and everything Jewish. Rav Kook zt”l used to say that we need to not complain about the darkness, but add light.] Now, to your question itself. The question stems from a belief that there is in fact a real Torah that Hashem gave to the Jewish people on Mount Sinai. All other systems of belief may be better or worse, but they are from man-kind. The Torah we live is a divine system, that has been in practice for thousands of years. When a person looks and tries to understand which set of practices is correct, they will see the vast difference between the Torah received by Moses and faithfully transmitted all these many generations, to systems that reject (parts or all) of the divine word, and replace it with human ideas. Blessings.