ᐅ Expanding a Two-Family House into a Three-Family Home – Looking for Ideas

Hello everyone,
we are facing the following “problem”:
We have an old house (foundation 9 x 10 meters (30 x 33 feet)). On the ground floor lives my mother (65 years old), on the first floor my grandmother (almost 90 years). The attic is currently used as an office. There is one main entrance with a shared staircase. The house has an unfinished basement. It was built in 1951.

We are a family of four and are looking for ideas on how to renovate/extend the house so that we can all live in it together. So far, we don’t have any perfect solution or clear ideas. For the roof, we would prefer a single-pitched roof. Maybe an extension in the form of a cube or a terraced house on three levels with (roof) terraces, or an additional floor (although we prefer not to increase the height of the house too much). We would rather extend the house in length and width than in height.

For our apartment, we imagine a large kitchen-living area, an open living room, a small guest bathroom (not mandatory), two children’s bedrooms, a bathroom with shower and bathtub, a bedroom, and possibly a storage room. Lots of glazing/window fronts. Ideally, our apartment would have its own separate entrance.

The great-grandmother’s apartment could be rented out at some point.

We would like to renovate and rebuild the house as energy-efficiently as possible (passive house standard, if possible). The plot is about 800 square meters (8,600 square feet).

Has anyone done a similar project or have ideas for the planning?
We appreciate every tip or suggestion!
Thank you 🙂