Hey, glad you're enjoying the character interactions! They're honestly my favorite part of the game to work on. I can't wait to do more between the girls as well haha, Sarah and Metatron in particular.
Ashley and Metatron... well, you might enjoy the next update if you're interested in that.
As for sex battles - the honest answer is that they're coded very poorly, take a lot of work, and (imo) all feel too similar. I have a plan to fix that in the next few months, but until then I don't want to add any more on the current, mediocre system.
Rest assured that Sarah will get a proper one, making full use of her various... attributes, when that gets fixed.
Group 'battles' will be possible then too!