House and garage - How best to place them on the properties?

Would it be possible to circumvent this according to your knowledge by officially merging the two plots?

If there are no clauses in the purchase contract, the OP probably has nothing to fear. Although intervention by the authorities would be possible under §176 Baugesetzbuch, which depending on the house placement would not necessarily be prevented by a plot merger, it is practically almost never applied due to the significant interference with property rights. Instead, clauses are common in the sense of: If you do not build in accordance with the development plan within one year, the purchase contract will be reverted.

Or doesn’t the merging have to take place anyway in order to combine the total area of both plots for the purposes of floor area ratio and plot ratio?

Floor area ratio and plot ratio are quite generously set at 0.4 and 0.8. I haven’t added up the m² now, but it obviously won’t be tight. In the case of realization of plan #15, a merger would be advisable due to boundary encroachment, but it could also be solved by an easement.
In #36 the option of later plot division was mentioned. With clever placement today, one could avoid that in the future.

Only the planned access via the "footpath" seems to be considered problematic by some.

But the concerns were about the destruction of a play street. OK, with two children, the parent taxi can already cause 16-20 vehicle movements per day, but I cannot follow the argument that use by one, maybe a second resident endangers a child-friendly living environment and disrupts the neighborhood relationship.

Really? I am. The paths are not only used by the homeowners. Usually, the children in the neighborhood meet on safe paths to play together. If these paths are also used by vehicles, in the end there will only be roads for cars. They park everywhere and you are not allowed to play ball or hide and seek there because something could happen to the little darling.

I cannot follow that the use by one, maybe a second resident still, endangers a child-friendly living environment and disrupts the neighborhood relationship.

It depends on the neighbors. IMHO, there is a difference between going from no motor vehicle at all to one or two or going from one to three. The former is, in my opinion, more serious. Do I understand it correctly: according to the plan, perpendicular paths run on the left and right of the property respectively. One is free for motor vehicles and the other is not? Then I would leave it at that and be happy that one path is free of motor vehicles and stays that way.

Really not? I am. The paths are not only used by the homeowners. Usually, the children in the area meet on safe paths to play together. If these paths are then also driven on, in the end you only have streets for cars. They also park everything up and then you are not allowed to play ball or hide and seek there, because something might happen to the precious darling.

That's how it is.
But it has always been the German mentality to claim the street in front of one’s own house just for oneself.

However, here the resident is actually considered the owner.

But it is not nice when all paths are being developed for motor vehicles [emoji6]

As can be seen, there are different opinions on the topic of the footpath. By car, at most we and the neighbor would drive on the path by car. We believe that there will be very little traffic in the settlement, as already described in detail—especially on the "footpath." Who else should drive there besides us and at most our neighbor? Then the children should just gather and play there, and if we come by car once, the children will step aside briefly and then continue playing. I don’t know it any other way from my childhood. It will not be a street where cars will speed at 50 km/h now.

The development plan has meanwhile also been signed by the mayor and was publicly displayed. It can be downloaded from the homepage of the city of Herne. If anyone is interested, I can gladly link it here.

To pick up the topic of the terrace again. The development plan states


Excerpt from the Building Code
(1) For urban planning reasons, the development plan can stipulate:
[I]7. the areas where only residential buildings that could be supported with means of social housing promotion may be erected in whole or in part.[/I]

If I interpret this correctly, the building boundary applies only to residential buildings, not to a terrace. I am not well-versed in development plans and the laws regarding this, but my assessment was confirmed by the land seller and a city official.