As for Samantha, you'll need to have her work in the bar and win a drinking game against the customer (you have to bet a private dance from Samantha).
As for Jennifer, there aren't yet sex scenes with Jennifer besides one cabin event, but if you've seen it, then you've done it. Actually, of the students, only Natalie can be fucked right now :D it'll change pretty soon as most of the introductory stuff is done, so it's time to crank up the corruption dial a bit.