Missing right of way: Do road construction and development costs pose a threat?

Hello,
I hope I am posting the question in the right subforum.
Due to our plans to extend my mother-in-law’s house (which is why I have already done a lot of reading here), we have encountered a tricky and potentially expensive situation that will probably ruin our expansion plans. As a layman, I don’t know if I am assessing it correctly or if my concerns are exaggerated.
I will try to describe the circumstances based on the site plan:

Imagine a residential area with a development plan in a municipality of 11,000 inhabitants in Münsterland, 800m from the center.
Kuhstraße comes from the bottom right and continues to the northeast. Eichendorffstraße comes from the north and ends where I wrote the street name.
The continuation of Eichendorffstraße to Kuhstraße does not exist, it is only a planned street. Parcel 952 already belongs to the municipality.
Parcels 947, 948, and 944 are partially developed (there should already be a sewer) raw building land. Currently, just a few horses are roaming there.
My mother-in-law lives in the house on parcel 953. The "hammer handle" to the planned street is simply meadow.
However, the residential building and the 3 empty plots do not belong solely to my mother-in-law, but to the community of heirs between her and her brother.
The brother, in turn, owns parcel 949 alone; his house is below. The building above was an old barn that burned down three years ago. A small part, whose outer walls still stand, now serves as a "carport." The section in between (in front of the mother-in-law's house) still visually appears as the "old driveway" of the house behind but was separated into the brother’s ownership 20 years ago.

As you can see, my mother-in-law’s house has no street connection. There is no right of way either, just a silent tolerance. The utility lines run through the brother’s land to Kuhstraße.

Next year, the community of heirs is supposed to be dissolved, and the mother should get the house and the 3 empty plots (the brother will get other parcels in return).
Because the brother said last year that he would give us a strip from the yard in front because he would be happy if we preserved his parents’ house, we thought about extending the house with the start of construction after the dissolution of the community of heirs.

But now the hammer came down: suddenly the brother says he won’t give anything and also rejects a right of way.

Does this mean for us that we can only get a building permit for the expansion by building the planned street along with relocating the driveway and the utility lines?
Which would cost almost €100,000 at once and kill the whole project.

Additional question:
Even if we don’t renovate and the mother simply takes over the house by division of the community of heirs, isn’t there a permanent risk that the city will become aware of the enclosed situation and start building the planned street at any time?
Could the mere division of the community of heirs alert the municipality and then the mother-in-law (as the sole owner of all 4 parcels at the planned street) gets the big bill she could never pay?
Would it then be total "suicide" to even submit a building application because that would explicitly put the situation under the municipality’s nose?

I hope you can help me or at least ease my fears a little. Or do you even have solutions?

Regards Thorsten

The uncle-in-law, the old sly fox! Sounds as if he had skillfully orchestrated everything.

Does this mean for us that we can really only obtain a building permit for the expansion through the construction of the planned road along with the relocation of the driveway and the utility lines?

Yes.

Even if we do not renovate and the mother-in-law simply takes over the house by dividing the community of heirs, does the permanent risk remain that the city will become aware of the enclosed situation and could therefore start construction of the planned road at any time?

Yes.

Might the mere separation of the community of heirs already be enough for the municipality to take notice?

I don't think so, since no sale takes place and the municipality is not notified.

Would it therefore be total "suicide" to even submit a building application, because that would explicitly rub the situation in the municipality’s face?

Well, at least two building plots would be created with the development, which could be sold.

Actually, it was not planned to give up the empty plots without necessity.

But how could it work out for us then?
Assuming we apply for the building permit in January/February. In April, the separation of the community of heirs takes place, then the mother transfers her house to us against the right of residence, with which we start the expansion.
Meanwhile, the municipality tenders the development of the meadow and has it carried out during the year.
After completion of the development, the invoice follows. Due to invoicing based on area shares, an estimated 40% of the allocated amount goes to us as homeowners and an estimated 60% to the mother as owner of the empty plots.
Now the payment is due within a certain period, the sale of the plots will certainly take somewhat longer than our payment deadline after completion of the development.
Do we have to finance our development costs from the outset with our construction loan?
Or would we still get interim financing despite the construction loan, which we could repay through the sale of the plots (even though the plots do not belong to us)?
Does the mother also get such interim financing despite a car loan, age in mid-50s, and rather low income?

Hopefully, the mother and her brother will take this disadvantage of about €100,000 into account so that one can really speak of fifty-fifty later, after all, he already received enough building land during grandma’s lifetime.

Well, we are not supposed to comment on your family stories here. Such a complicated credit structure should rather be considered commercial and thus played through with the house bank.

What is there to say as an outsider about such family entanglements? He already has enough, the other one is backing out, Mom is supposed to do that ... ohauahahuaa. Take a few thousand in hand, get a consultant, fix the result in writing and at least shake hands on it.

But how could this then proceed for us?

You urgently need to talk to the municipality. How old is the development plan? Is it available online? Does the municipality even want to develop the area? If yes, when? How high are the estimated costs? Which property owners have to participate? When must payment be made? Why do you want to release the uncle from the obligation, or was the proposal to dissolve the community of heirs made by him? How could the current situation arise at all? Why were the rights of way and utility easements neither secured in the land register nor under public law? Who conducted the parceling of the property how many years ago? Are there written agreements regarding the community of heirs? Was there a will at that time?

"the old farm entrance" of the rear house, but it was separated into the possession of the brother 20 years ago

The parcel numbering does not fit with that. When, how, by whom and why were the parcels 943-953 created?