Nadech didn't choose Yaya cuz she is his kookwan, it's more cuz she is one of the close friends of his
I got to know that Nadech got to choose his own guests, there was no force or whatsoever that made him and the rest of the boys choose their own guests
At first, Ch3 made it look like the boy would invited their N'eks
but it turned out completely different. Their guests were unpredictable which was good, it made the concert look more fun
Mark got to play Kawe with Anne. Boy personally chose Aof. It was leaked by Yadech's fans weeks ago that boy would go for Aof
I think the boys got to choose but it had to accommodate the guests' schedules and such