Our idea is to divide the property into 2 different units:
(1) 1-bedroom apartment that has a bedroom, a bath (located in the existing bathroom), living room and kitchen-dining with open concept. The living room has a sofa bed that can occasionally transformed into a night bed for guests.
(2) 2-bedroom apartment that has 2 bedrooms, a shared bath (new one but it is basically near the existing bath, so the plumbing can be extended from there), and open concept living room and kitchen-dining area. Living room has also a sofa bed for occasional guests. This unit can also have 1 bedroom and 1-study room, if preferred.
Our design principles are basically focusing on creating open spaces, preserving most of walls, columns, and plumbing system. The openness of each apartment can give more flexibility, in case the units are going to be reshuffled again or be joined into one again in the future.
Hope that our plan study will contribute some ideas for your project. Thank you for this opportunity!