I think that before the I LAND, Belift Lab did a global audition for I-LAND program and so technically I-LAND participant is Belift Lab's trainee until they officially came to I-LAND. K did say "trainee", they must have stay together as I-LAND participant from Japan prior to coming to I-LAND. After all, they still need to learn Korean Language as I-LAND participant from Japan. TA-KI and NI-KI enter through Belift Lab Global Audition in 2019 and their I-LAND profile released by Mnet did say that K has trained for 2 year 8 month, TA-KI trained for 10 month while NI-KI trained for 8 month. I assumed this "trained" profile refer to their training period under Big Hit and Belift after auditioning before I-LAND kick off.

no, during their trainee period lol. K explained that Niki and Taki's practice would end at 5pm due to their young age and his at 11pm. So they'd wait after till K was done. Being a trainee doesn't mean you're locked in the company building 24/7. You have lessons/classes and personal practice time on certain days/times. But besides that, you live a normal life going to school, your part-time job, going home, etc.

Trainee live in a dormitory