Is a development plan required for obtaining offers?

I don't believe the municipality wants to establish a development plan here anymore. I think the property is buildable from now on according to §34 of the Building Code.

That's also how I would assess it.
Am I correct in assuming that building "16" is the new kindergarten?

In view of the planned development, the boundary layout could have been somewhat fairer.

If a 16 m tree removal boundary must be kept clear from the street, I see the unequal plot shapes as less dramatic.

But that doesn’t look like farmland.

The house at the top (which we are currently living in) has been there since the 70s and is logically building land, otherwise no house would stand there. The rest of the garden including our area is actually farmland. I don’t know why it’s regulated so strangely here, it’s probably something inherited from earlier times. A few hundred meters further up (not visible in the picture) there is another neighbor, and the same regulation actually applies there as well. The area around the house is building land, the rest of the garden is farmland/green space.

What was decided? The amendment of the land use plan, the adoption of a development plan, or the expansion of the inner area, or...?

I can gladly quote the publication here once:
Inclusion statute for the XY area – Announcement of the resolution to initiate according to § 2 paragraph 1 of the Building Code
(...concerns parcel numbers XY, so ours + the area of the new kindergarten...)
The inclusion statute is intended to ensure an orderly urban development between the existing buildings and regulate the construction of a forest kindergarten in the northwest area.

The resolution to initiate is hereby announced in accordance with § 2 paragraph 1 of the Building Code.

I don’t want to sow discord among the siblings, but it looks like only your brother discussed the new boundary line with the surveying office.

If a tree-felling boundary of 16 m must be kept clear from the street, I see the unequal plot shapes as less dramatic.

No no, it was already agreed like that, as 11ant says, it was intended that way because of the tree-felling boundary. And that was the only way to really divide the inherited plot 50/50 so that two separate houses can fit. We are not allowed to build directly at the street anyway. It should be mentioned that my part at the back is a bit wider and I also have a long notch at the bottom, which makes it large enough. A straight division right through the middle unfortunately wasn’t possible.

I can only say that about a year ago, the building authority verbally told us in a meeting that the whole process from farmland to building land would take about a year (which is now almost over).

That’s how I would assess it too.
Am I right in assuming that building “16” is the new kindergarten?

No, actually not, but directly to the left of it, but still on the property (which was previously farmland as well). Building 16 is an old city building, a clubhouse.

Announcement of the resolution to establish in accordance with § 2 para. 1 of the Building Code

It should actually be § 3.

Incorporation statute

See, no development plan. Your property is declared as inner area by statute (§34 (4) 2 or 3, Building Code). Were there no further related public announcements in the meantime? If the kindergarten is already standing or under construction, the statute should already be legally binding.

It should actually be § 3.

Unfortunately, I can only copy what is written there, I absolutely have no knowledge in the construction field to my shame. :D That should of course change.

There you go. No development plan. Your property is declared as an inner area by statute (§34 (4) 2 or 3, Building Code). Were there no further related public announcements in the meantime? If the kindergarten is already standing or under construction, the statute must already be legally binding.

Oh really!? In preliminary talks with companies, a development plan was always fundamentally required as soon as we said in which city we want to build! That basically means we just have to wait for the next announcement and from then on we basically have the "go"? Where can we find out which regulations we have to comply with without a development plan?

Unfortunately, nothing further so far, we have been diligently checking every announcement in the newspaper for months, nothing there. The kindergarten is actually already standing, it was built in an expedited procedure due to a shortage of kindergarten places. They are just construction trailers, so not a proper building, which is why it probably went quickly. The building authority told us that we are in the normal procedure and the kindergarten just has a special regulation and therefore benefits from the expedited procedure. :(

Oh, really!?

I don’t know. The procedure seems to me to have been taken up somewhat hastily by the municipality. §2 (1) speaks in favor of the establishment of a development plan, while the word "Einbeziehungssatzung" argues against it. The reluctance of the authorities’ staff to provide information indicates legal uncertainty.

If your city is equipped with all the responsible bodies (planning office, building regulations office), then the planning office must be able to give you a binding statement about the current planning law, including the status of any ongoing procedures, and the building regulations office about which other regulations must be observed for your building project (BayBO, neighborhood law, surveying and cadastre law, forest law, ...).

According to your quote, at least the establishment of an Einbeziehungssatzung has been decided by the city council. After that, the resolution for the public display of the statute should follow or may already have followed, and after one month the statute resolution. Whether the establishment of a development plan has also been decided in parallel is possible, though unlikely.

In preliminary discussions with companies, a development plan was always basically required as soon as we said in which city we wanted to build!

The companies will hardly be informed about all ongoing procedures in the area. They simply request the standard documents from the client. Find out which offices are responsible for you in terms of planning and building regulations and ask there again precisely.

They are just construction trailers, not a real building, which is probably why it went quickly.

Even the installation of "temporary structures" is not allowed in the open countryside without further ado. It probably didn’t go quite correctly, which is why they are now very reserved.

that we are in the normal procedure

Whatever that is supposed to mean?

special regulation

... means "Kölscher Klüngel" for us.