The bigger issue I have always had with Kira is the idea that she would be not just willing but seemingly eager to help Max fuck his own mother and sister, even going so far as giving lessons in anal sex to her own niece and nephew. There are plenty of more believable ways to set up the sex scenes with the rest of the family (believable for a porn game at least). I still like the game but it pretty much requires so much suspension of disbelief that you have to basically just assume that everything is going to be completely ridiculous and not really have any plausible justification. It's not quite as bad as blatant mind control but it's pretty close.
Olivia is a perfect example of a plausible way to develop Lisa's path. You have a girl Max is not related to that Max can have his way with and it would make complete sense for Lisa to have a front row seat to that and be turned on by it so you could set that up to escalate in a more reasonable (for a porn game) manner until she joins in.
I actually have very little issue with Kira setting up Ann. Kira has basically been the bad sheep of the family and disapproved of even by Ann for her choices, so helping Max is Kiras way of proving to Ann and herself that Ann is just as flawed.
Ann could take the moral high ground and find another way (she tries this with a maids job in one of the versions) but this is Kiras version of the Jokers "one bad day" faced with a similar situation Ann would be no better than Kira (and is arguably worse)
I could make a case that the sisters are levers to help move Anns moral compass but that seems rather sociopathic the alternative being that they are more like collateral damage and as long as everyone's having fun why stop the party.
Olivia is a bit of an issue, Max hooks up with Olivia, happy couple and occasional threesome with Lisa and ... there's no linkage to anything else that's kind of End of the game Max with Olivia and maybe Lisa, Ann with Eric and Alice with Kate.
There's sort of a route into Alice via Kate and Max's Voyeurism but Ann is a very hard route to work to
Unless you go the Eric sex slave route with Olivias mum and then there's a whole new set of headaches
As an asideI always find it interesting Eric gets everyone bent out of shape (either for or against) but no one cares about exclusivity with Kira who's off doing porn movies half the game