I doubt they will allow you to check in together but it won't hurt to try. The ability to check in together as you want to do is not a *A benefit nor a TG benefit. If the counter was next to their Y counters and the C counters weren't busy then they'd likely allow it I would think, but the C checkin is in a different area and has fast track exit immigration at the end of the row. I guess that TG needs to pay for the fast track immigration so I doubt they'll allow it.