Construction ancillary costs not visible?

For me, it initially reads as if far too little information is provided by the OP for even a single user to offer concrete assistance ;)

Rhenish greetings

I was purely concerned with this structure:

There are a total of 2 semi-detached houses as well as a single-family house. Behind them, a multi-family house is being built, which will not be sold but will remain owned by the developer.

Not everything is always taken that precisely and much is lumped together. I also hardly believe that any volume discounts will be divided. They will nicely remain with the multi-family house. ;)

Will we ever find out what this is about? At least at IS24, I couldn't find any project with these facts by googling.

either it is a property developer and the amount to be paid is already notarized down to the last cent, or it is a construction company and one pays the ancillary costs anyway. whether the construction company handles the administration or you do it yourself makes no difference. of course, it may be that the construction company in turn makes a fixed price offer (e.g. €15,000 for planning and execution of house connections). but as long as grass and hedge are referred to as ancillary costs here, the whole question is confused anyway.