I did it it last month with my little cousin in BKK.
I was in F and he was in Y (no status). We were on seprarte tickets also. and we both checked in together at the F section- No probelm at all, even managed to get him an emergency asile (31C on B744) seat. Afterwards we took the mini-2 seater electric car to the F lounge together.
So if they allow Y pax to check in with F pax (2 class diff), I guess Y pax checking in with C pax (1 class diff) should be fine also.