It's a "no", pretty sure they're not allowed to say that they are. Although if that's the case I don't know why they didn't just not respond, since that's what I would have done to maintain the fantasy.
My standpoint is IF they are maintaining that none of the characters are related, then they need to rewrite the text and dialog to remove all the "it's so wrong! A landlord or roommate shouldn't do this!" as if they are trying to push the incest fetish, when NO ONE is related.
Don't half-ass shit, either it's incest, or it isn't.
What if it was never about incest? Maybe they're insinuating, "It's so wrong," because the landlady is technically in a position of power over the MC? Maybe the roommates make the same claim out of fear they may be evicted due to a contractual obligation to abstain from sexual relations with other flatmates?
The developer's vaguery is quite clearly on purpose, most likely because content featuring incest would bar them from both hosting the content and receiving monetization on sites like Patreon or Subscribestar. While it being a social taboo given center stage in a game might seem insignificant because it's just a game, it's still a social taboo.
At the end of the day, the suits at Patreon are gonna look at the content being hosted on their site, then look over at the investors looking for a payday. They want safe investments and Patreon knows this. If the mob on Twitter gets ahold of the news that a piece of content is glorifying something like incest, what happens to Patreon's image? Certainly doesn't sound good to an investor looking for a fat payout, so it especially doesn't sound good to Patreon -- hence their policies and ToS they've implemented restricting that kind of content.
I've seen a lot of comments on this site with frustrated people throwing their fist in the air and damning the creators, but y'all need to understand that half the time it's not up to them. They're just doing what they can to make something enjoyable for us and them, even if that means skirting a couple lines here or there just to stay under the radar. If you can't use your imagination and fill in the blanks, that's on you.
While I'd concede to the idea that it certainly sounds simple, nothing in life really ever is.
What we're seeing here is compromise -- a concept lost on many today. Rather than completely throw in the towel, they're playing with a loophole that will allow them to put the main character into a loosely reasonable situation without treading on the boundaries set by Patreon. The author's intent should be apparent, but considering they haven't explicitly stated that it is in fact incest, it still leaves them open to be able to host their content while receiving revenue. Does this mean they have to sacrifice some details in the story to abide by these rules? Yes, it certainly does. Does it mean you, the player, understand the implications of the situations described any less? As far as I can tell, no, it doesn't. This one detail is easily surmounted by the player's ability to understand context clues and know that maybe something else is being implied.
Crafting a detailed storyline and a complimentary world takes a lot of time, which is something that doesn't come cheap. The developers are still people with financial and physical obligations just like you. They want to be able to create something that's well worth your time and theirs. Knowing that it takes time and dedication to do so, the most rational route would be to monetize that time spent making the game. I understand it can be frustrating having the characters ostensibly portrayed as roommates, but if they hadn't written it this way they most likely wouldn't have been able to deliver updates at this frequency with this level of polish as just a small team.
The barrier to entry for this title is as small as the suspension of your disbelief. If the idea of them dancing around the subject matter to remain on the platforms that allow them to operate in the first place is this much of an issue, there's other games out there that explicitly state that incest is one of their themes.