IIRC, all of these options -- loungers, beach bed, bungalow, and cabana -- are based on one person buying them and then indicating who else in his/her party will be using it. So if you need a total of four then you only need two people to buy them, total cost $90.
That said, I still think that with a party of four or more, going the bungalow or cabana route is much better in spite of the higher cost. You have guaranteed shade, the cabanas actually have a ceiling fan installed to keep you cool on a hot day, and the attendant taking care of you just makes it a nicely indulgent beach day. Now, if you think you'll spend 90% of your time away from the place and hanging out in the water or doing other things, then the loungers may be more than enough.
Thanks @WAAAYTOOO ! I've been reading this blog for tips and ideas since we booked it a couple weeks ago, figured it was time to join up. For the price (2 staterooms/4 people, prepaid grat, and deluxe drink package for about $900pp) I think this will be a perfect first cruise for them. Not too big, but not small. Should have plenty to do, especially with these upgrades. Want to get them hooked so this is the only way they want to vacation from now on!