Nope, they don't. If on the same PNR, one person can check in both persons and receive both boarding passes - no problem. For that matter, even if on separate PNRs, you can check someone else in if you have their credit card or even just their PNR locator. Heck, you can even check them in online with their MP# & PNR or p/w. You will need ID for baggage though if you exceed your allowed pieces for your ticket (ie you can check in all the baggage on your name, but if you have more than you're allowed - 3pc for example - you'll need their presence & ID to check the bags under their name too).