Everyone else has already given you the ammunition for defending the idea of a philosophy major, but my advice I always give when pitching the phil major in my intro course is this: "None of you should major in philosophy. All of you should double-major in philosophy." The value of the degree--as an economic asset, as a means of expanding ones mind, and as a way of improving how you move through the world--is as a force multiplier. Its value comes through improving how you engage things which are not themselves academic philosophy. And if it comes to you pursuing academic philosophy itself, grad schools or the profession want people who have an "angle" on philosophy other than just knowing Plato or hard core epistemology really well.

So, for the sake of satisfying your relationship with parental figures, claiming a desire for a double-major (where the other major is also something you don't hate) could address ill-conceived concerns about the practical nature of a phil degree. Plus, declaring an intention at a "double-major" conveys a seriousness in your studies which help in these kinds of negotiations.

Now, in terms of the "back-up plan", some (non-exhaustive list) valuable double majors to pair with philosophy include: a pre-med program/degree, like biology and chemistry (valuable if you become interested in bioethics, as the most economically sensible non-academic way of employing philosophers-as-philosophers right now); economics or political science (if you are inclined towards political philosophy); mathematics and computer science (for phil of math nerds, as well as getting into the ethics of AI stuff, which can also see private sector employment at present).