Damn you got me with the dads! That the MCs were half-siblings was indeed something I suspected already, then the door open, I was like whaaat! And then the twist.. or maybe anti-twist? I cannot help but wonder if there is more to it. How much have you and Drifty cooperated really? I will have to get started on u4ia and see if there is more there...
Oh, by the way, in one line this MC is wondering about his step-siblings, but what he actually wonders about should be half-siblings, no?
It's a few scenes later, just after the girls and Artemis are chatting in and by their pool.
"Kapuletti's safehouse
A few hours later"
MC and the dog.
"...."
"(So, my old man was a modern-day Genghis Khan before meeting mom.)"
"(Makes you wonder if I've got any step-siblings running around out there...)"
And if the rest of what I wrote is confusing you might want to play/replay "Leap of Faith" which has.. a few interconnected references with Artemis that seem random if you've only played the one game, but is hinting on possibly rather important stuff if you've played both.