I do believe the focus remains on the main characters, the couple you mention do appear as supporting characters to keep the main characters plot moving, do you feel I might've perhaps have slipped regarding the core themes of the novel with their introduction friend?
The main reason why they're a lesbian couple instead of another friendly couple it's because it's a bit of murky territory anytime one adds a new character to a game like these
You see my friend, when I first started despite me insisting, reiterating and boldly enunciating that the game was focused on one sole Love Interest and that there'd be no harem, couple swapping, NTR or anything of the sort. I still received quite, quite the.. let's say harshly worded reviews and feedback on my PMs
There was even one man who for a while (until our swift moderation team here in this forum acted) just kept posting and spamming about how what the game truly needed to thrive was the introduction of a black man to cuckold the MC.
Then in one episode I added a african american woman who I believe didn't even have lines. She was just shopping in the background, serving as eye candy.
I, once again, received a bit of hate mail with one that stood up to me particularly that said "Don't ever include any dark skinned character again for their presence in the screen made me go soft"
And as I say, she was just in the background! And if you know my style, this woman was logically designed to be appealing.
Now, while I understand we all have our pet peeves (I shan't be the one to cast the first stone for I have my fair share) I do find it odd when such events occur
So the main reason they're lesbians as I state, it's mostly my friend (and I assume this goes for many other novels out there) because if you include anything but women. It's inevitable that you'll get two kinds of comments.
Some folk dooming about how NTR is now inevitable. And some other encouraging such a thing.
Even when one such as myself has stated from the beginning this is a single Love novel. You're only with your sister, nobody else.
And still when the boss character was introduced, there was once again a bit of a.. torrential flood of varied and colourful inputs.
So while I do see your point, lesbians in VNs are a bit of a tired cliche. I do believe that after all this time making their main friend group two lesbians was the right call, for it has allowed to advance the plot with minimum offence caused to anyone.
In any case, I hope that despite this trope. You were able to have a good time, I sincerely do, my friend.
And if this were not the case I do still wish you may find some dream where you feel nothing but fullfillment.
Have a wonderful day, may you enjoy the times to come