I also have never had any problems checking in with my family who are all non-elites. We mostly fly DL or one of its partners and even when I'm not travelling, I've been able to check them in at the first class / medallion counter. However, I did have one bad time when I was travelling with BA from LHR Terminal Four. I went to the "Late Check-in" line which was empty and attempted to check-in. After initially refusing to check me in, the clerk was convinced and finally checked me in. BA may be more rigid with its rules and procedures than most other carriers.