It's clear from context that Beniko's books are about gay romance. Reading the book helped him understand what his daughter is feeling.
Honestly, I don't think they are, with the exception of the book inspired by Yuki. Considering Yuki's love for her books but lack of any real concept of same-sex relationships for quite a long way into the story, they are more likely still mostly straight romance. What makes her books stand out from the rest is not the gay angle, but rather the empowering feminist one, as it is pointed out that the women in her books choose to live and love how they wish.