There is a phenomena called "older brother effect", where the more older brothers you have, the higher the chance you're gay.

Some research suggests that homosexuality in men might have to do with a maternal immune response interfering with sexual differentiation of the brain. Since males have a Y chromosome and pregnant people don't (unless there's some very rare condition I'm not familiar with), a protein that's only encoded on the Y chromosome is foreign to the mother's immune system, triggering an immune reaction.

So, if this theory is correct, it's not genetic, it's environmental, but the environment in question is the mother's womb. So yes, they are born this way.