With very minimum change of the existing plan possible, I joined these 2 apartments with maximum functionality.
I choose the entrance at the right side from the lift lobby to have a better privacy from the outside area.
From the entrance, I directly put the open space for living and dining area. This space will be bright and feel spacious due to the open plan. The kitchen will be in the existing kitchen from apartment 2. Mostly, the layout of Apartment 2 remains the same, just little modification on the bathroom to make some laundry space. The 1 extra room at apartment 2 can be used as a home office, which can also be converted into small bedroom when there is child 2.
On the apartment 1, the existing living room is converted into master bedroom with a balcony, and the existing kitchen will be for the wardrobe space. The main entrance of apartment 1 is closed, makes a more private access to the master bedroom.
There is 2 bathrooms inside the merged apartment. 1 larger bathroom near the master bedroom which has the bathtub as well as shower, and a smaller bathroom near kids' bedroom which uses shower.
In the future when the apartment intended to be sold, it can be easily converted back into 2 units of apartment without too much works. :)