Expanding a two-family house into a three-family house - ideas wanted

Hello everyone,
we are facing the following “problem”:
We have an old building (foundation walls 9x10 meters). On the ground floor lives my mother (65 years), on the 1st floor the grandmother (almost 90 years). The attic is currently used as an office. There is a shared front door with a staircase. The house has an unfinished basement. The year of construction is 1951.

We are a family of four and are looking for an idea on how we could remodel/expand the house so that we can live in it together. So far, we lack ideas or have not yet found a perfect solution. We would like a shed roof. Possibly an attached cube or the house terraced on three levels with (roof) terraces, an additional floor (but we would rather not let the house become that tall). We would prefer an extension in length and width rather than in height. For our apartment, we imagine a large kitchen-living room, open living room, small guest bathroom (not necessarily), 2 children’s rooms, bathroom with shower and bathtub, bedroom, and possibly a storage room. Lots of glass/window fronts.
Ideally, there would still be a separate front door to our apartment.
The great-grandmother’s apartment could possibly be rented out at some point.
We would like to renovate/remodel the house as energetically efficient as possible (passive house standard if possible). The plot is about 800 sqm.
Has anyone had a similar project or any ideas for planning?
We look forward to any tips/suggestions!
Thank you :)

We appreciate any tip/suggestion!

Plans of the existing building? Development plan? Legal requirements? Is a 3-family house even allowed? Desired living space? Budget? Passive house standard as standard = that will be more expensive than demolition and new construction (with 9x10m existing building + your extension, it can go into the seven-figure range).

Budget max. €700,000 No development plan exists. Desired living space approx. 130 sqm 3-family house possible (as the neighbor has also recently converted 3 apartments)

...Extension and bring the rest to Passive House standard? Tear down the shed, build a new one, probably saves a seven-figure amount...

Ok, just difficult with great-grandma… difficult situation

Budget max. €700,000 No development plan exists. Desired living area approx. 130 sqm 3-family house possible (since the neighbor recently also converted 3 apartments)

Then off to the architect and energy consultant. The extension will cost half a million + architect fees. But then only normal energy standards. You can use the rest to renovate around. But a renovation, and then to passive house standard, never ever...