I think the question is why/how the sexual orientation is relevant. The same as skin color etc, that seems irrelevant to me.
Only white, heteronormative, neurotypical experiences influence the creation of artistic works. Duh. /s
In this specific case what makes the discovery of a grandaughter of the author a massive surprise and plot twist is that her father and only child of the author was gay. Had he not been so, expectations on the existance of a living descendant of the author might have been different.
That’s what makes his sexual orientation be relevant in this case: it explains why nobody expected there would be living descendants of the author and why her discovery was such a massive plot twist.
Had her father been, for example, a catolic priest (quite independently of sexual orientation), that information would’ve been relevant in just the same way and for the same reasons.
Whilst I agree that people’s sexual orientation is irrelevant in most stories that aren’t about romance (and no matter which way it goes, by the way), in this specific case it absolutelly is relevant to explain the behaviour and expectations of other participants in the story up to the point when the grandaughter was discovered.
Straight people often (don’t) have children. Assuming that it must be this or that, forever, is absurd.
In America, race and sexuality being irrelevant is a privilege of straight white men. When someone has done you violence because of who you are, you’ll spend every second of the rest of your life with who you are and how likely the people around you are to try to kill you over it in the forefront of your mind. When I, as a queer person, walk into a room I immediately sort everyone in the room into threats, allies, and people who will just stand off to the side because experience has taught me that if I don’t some people will beat the shit out of me and others will tell me that I deserve it for “being a f*g about things”. Ask your black friend, or your gay friend, or your woman friend. I guarantee you every one of them is more on guard than you because race, gender and sexual orientation will never be irrelevant to them.
That’s fucking terrible. And another reason not to make something like that public, when it is that prone to be used against that person.
The last time I was bullied and attacked was back in school. Kids don’t need any reason to be hostile, it could be the angle of your eyebrow.