I'll make a quick guide on how to get the pool content from the very start, for clarification...
Ken email -> visit Ken, agree to photo (Invite to house) talk to Samantha in Bedroom and say he's a cool guy
Thursday -> Hallway -> Garage -> Entrance -> take photo, select dialogue that has (Sharing Route) this is a trigger for later dialogue and is important.
Visit Ken and Samantha often, do the hacking game to improve her relationship with you, eventually she'll ask you to go to beach with her
Samantha should be friendly enough at this point you can take photos, take photo of her at beach and at home. Ken should have virgin dialogue, select Samantha.
Continue visiting Ken/Samantha, you should be able to show Ken photos. Samantha should offer sex, agree and during her nut sucking, there should be an option to take photo.
Next visit should prompt showing Ken the nut sucking picture, he should say he's ready. Talk to Sam and she'll be hesitant regardless of selection. Back to Ken, and agree with what he says (Can't remember the dialogue)
Visit next day, and fuck Samantha. Ken will join in, and there will be dialogue. At some point (Might need a return visit) there will be talk about Ken joining at the beach, he'll say he can't swim.
Pool content should now be unlocked. Go to the public pool, there should be a new option to rent out the pool for $3000. There are several scenes, all costing 3k.
Sorry for the long post.