I'm planning a trip with my employees! I'm torn between Southeast Asia, Japan, and Jeju Island

It's me, 3 employees (though they are actually family, friends, and a younger acquaintance),
my wife, and a 22-month-old baby—6 people in total.
I'm really struggling to decide where to go ㅠㅠ
I want to go to Jeju Island, but it seems like everyone else wants to go abroad.
I feel like we'll have to walk too much in Japan,
so Southeast Asia would be better, right?
If possible, could you also recommend some resorts?..
The budget is 4-5 million KRW.