Sounds like a question for the nice folks at Delta (1-800-323-2323 I think). I was only able to print out my own, then had to log on to DW's, DS's and DD's accounts to print their's.
Now Song tix are a different story (even tho they are parts of the same corporation). On the Song website, I was able to print all the boarding passes for our entire party.
Of course, when you get to the curbside checkin, all they needed was one of the boarding cards to check us all in, then I think the issued us new ones, I think. Check with the nice folks at Delta or Song either way. I have always found them a cut above the usual customer service folks, and the Song folks are even better..