You each get 22.5GB before you may get throttled... that's 22.5GB per line. And there's no guarantee that you will be throttled... we've gone over that amount multiple times with multiple lines and no one recalls ever being throttled... it only happens in congested areas, so not much to worry about. We've been with AT&T for over 15 years - from at&t > Cingular > AT&T.
Yes it’s each line. I have 7 lines, my sister used 109 gbs by herself last month. That is one good thing I have to say about AT&T. That’s the only thing tho lol.