Inherited house - and now?

Hello forum!

After Grandma's usufruct right expired, we have an unoccupied semi-detached house and face the big question: what to do? Tear down + rebuild or (core) renovate?

What we know:

[*]The house is 90 years old.
[*]There is a damp rubble stone basement.
[*]We had an architect come through who showed us what might be wrong. For example, he picked out a piece of steel beam from the basement ceiling/house wall with his fingers, which I find extremely worrying as a complete layperson. The houses in the neighborhood are all just as old, and none have been torn down so far, nor has any collapsed. I cannot really assess this "the steel beams will eventually become puff pastry" info. He advised against a small renovation, calling it a bottomless pit and said it would end up much more expensive than planned if something unforeseen happens. He threw this number at us: €300,000. For both core renovation, as well as a new build, and also for selling the whole thing. The latter is not of interest for now.
[*]Electricity/water pipes/heating would all have to be replaced.
[*]A call to the building authority revealed that there is no development plan. So basically anything is allowed for now.

Not visible in the picture are two garages on the right that are still in use and could initially remain untouched.
What it looks like under the house’s facade is unknown.

What we don’t know:

[*]What we want.
[*]How we should proceed.
[*]Whom we should turn to.

We would be very grateful for ideas of all (!) kinds. Things like, do you need a basement, do you build an additional rentable apartment as retirement provision or – the opposite –, can you leave out a floor because that would be cheaper, …

We are two, around 35, childless and petless, but that could look different in 5 years. Unfortunately, the lottery win has not come yet and we cannot replace the little house with a castle. Rather, we would like to stay under the architect’s estimated budget.

So. Who has an idea, an opinion, a stimulus for thought, or another question?

You obviously don't want to sell. Then the question arises whether you want to move in yourselves or rent it out. What do your current financial possibilities and your own living situation look like? From the outside, the house doesn't look that bad, there are completely different ruins that are not yet that old. If the house would actually fetch 300,000 EUR upon sale, I would probably sell it too. But I can't really imagine that if the need for renovation is supposed to be just as high. Was the architect also an assessor for such properties? Is the value of the land that high?

You apparently don't want to sell.

Oops...

What we don't know:

[*]What we want.

As a retirement provision, one builds an additional apartment to rent out

... I read from that that the living space is not needed for oneself

I understood it to mean that a second residential unit in this house is being considered. As an alternative, it is mentioned whether one could omit a floor in the possible new building.

Now I am curious about what is actually needed or meant

Oh, I forgot to mention that? We want to live there ourselves! What I meant was: whether one builds an additional apartment that could then be rented out. Or else builds everything small for ourselves so that it stays affordable. Maybe the real question is: how cheaply can one build? The architect is also a building expert and the only value is the land. Although there is also a potential buyer who would completely renovate the house instead of demolishing it. Yes, the interested parties come just like that, without it even being offered for sale...