I theorise that in the cuckold route this is a likely scenario, but also one for the sharing route, albeit it would be a choice made by the MC there. On the sharing route, esp. if MC and Julia shared their fantasies and have high CP, it is very clear that both are on the same page what this sharing/swinging (with Jasmine in the mix) is about. It might get to the point that Julia becomes pregnant and Jasmine too, but only by the choices done by the MC.
It might "simply" become a temporary threesome/foursome, maybe more. As said, depending on choices. Whereas the cuckold route seems to develop into the direction you mentioned going by the last update.
As for the promo pic: It looks very much like the sun/pool deck of Cornell´s house. I doubt this pic is from a holiday trip.