I have two groups.

Group 1 (3 people) – Delta to ICN. Korean Air to Hanoi. Two separate tickets.
Group 2 (2 people) – Air Canada to ICN. Korean Air to Hanoi. Two separate tickets.

Both arrive between 4:30 pm and 6:30 pm. The Korean Air flight is the next morning at 8:30 am. We are staying at t he transit hotel in the airport. Delta says they cannot link the tickets so baggage can go all the way through. Air Canada is TBD.

On the return, Korea Air says they cannot link to either Delta or Air Canada. One layover is 4 hours. The other is 8 hours.

How can I avoid customs and immigration and simply send my luggage to the final destination?