To me this is a no-brainer as a combo, BTW - you head on down to Old Fashioned Donuts and do the apple fritter for breakfast, plus some excellent donuts (you could actually eat there, though I never have myself).
And then for lunch you head back up to 69th and go to Uncle John's, for IMHO by far the best bbq in the city. I dont think the hours are unpredictable either, really - theyve just changed a couple times (for example, they used to be open till midnight and then 11 - the old menus still say that - but their closing time has moved to 10pm for a while now, M-Thu). But, if neccessary, you can always call and check.
Make sure to try the hot-links - your friends from Sonoma will have never eaten anything like it, IMHO.
I agree that soul food would be another fine option for an "new to them" cuisine. Army and Lou's is a pretty solid option for this, as suggested (though my own favourite is actually Macarthur's on the West Side - another place you can have a fine sit-down soulfood meal). And then there are a couple other rec's which I havent gotten to yet.. Turner's Family Soulfood (at 8233 South Ashland) comes highly recommended, and, of course, the now famous BJ's market has supposedly a fine soul food buffet.
(One of my own fave places on the southside, BTW, is a sit-down meal spot.. Uncle Joe's Jerk Chicken, on about 8200 Cottage Grove. If Carribean food is exotic enough to have not been tried by your friends before, this would be a great option too - great smoky Jerk Chicken with fiery sauce on the side, plus curry-goat, fried plantains, calalloo et al).
c8w