Actually, I think originally Deep intended for Anna and Rebecca to have fun together. The very first beach scene has Rebecca pretty much suggesting that she join Carl and her in a threesome. And in the second beach scene, Rebecca insinuates that her love for Anna, was not just sisterly but sexual as well. And you can decide whether Anna feels the same. Both these scenes appeared to be setting up future full-on sexual scenes involving Anna and Rebecca, and Anna, Rebecca and Carl.
But then of course, Patreon changed their rules on incest content, and all that went out of the window. For a while, even after the rules changed, Deep was still insisting that Anna and Rebecca would be having naughty fun together, because I think he believed that lesbian incest wouldn't be a problem. But by the time we reached Chapter 2, and Patreon's position was clearer, he obviously decided it wasn't worth rocking the boat, and that content got quietly ditched. He had them making out a bit, and giving Michael a BJ together, but that was as far as it went.
And the Anna/Rebecca/Carl threesome was kind of hinted at, during a scene with Carl, if Anna asks for his help with Earl, and Rebecca pretends to be asleep and spies on them. But it never went any further. I'm sure that was a combination of the change in Patreon's rules and the subsequent decision to make Carl into the game's chief villain.