Contractor / Alternative Subfirma

The VOB stipulates:

§6

Execution deadlines are extended insofar as the hindrance is caused by... force majeure ... The contractor must do everything that can reasonably be expected of him to enable the continuation of the work.

And the attempt to find another subcontractor is reasonable. Cost increases for the contractor in this context are not fundamentally unreasonable either. It strongly depends on the individual case.

Everything is bad, you are already behind schedule...

But the answer on the subject of [„Ersatz“] will again be negative if the construction company gets into construction delay due to force majeure.
I don't think you have any options there, unless you waive the service of the GmbH and buy services yourself.
But I could be wrong, it's layman knowledge.
Can't you have a lawyer work on this question? It would be legally secure and should be able to be clarified in a cost-transparent appointment.

With very high probability, the pandemic situation will be considered force majeure. Proving the opposite takes longer than finishing the house late. Your contracting partner is also interested in completing the construction site – there will certainly be an attempt to find other subcontractors. If these cannot be found at the desired time and at acceptable costs, you can stand on your head, complain, sue, threaten, or keep calm: you will have to live with the construction delay in fact and provide additional budget for the delay consequences to be able to move in. Whether you can get it back afterwards is another chapter.

Conclusion: right now and at this moment, it matters less what exactly your contracting partner "must" do, but rather what he actually does and what way you find together to move forward.

nur sind wir in eine Komfortzone geboren worden. Wir kennen keine Umstände, alles muss laufen, wie es uns passt

Thank you for these words – they speak very much from my heart.

That is force majeure. Construction sites of the federal government have already been closed for this reason. If you choose another company, you will be liable for damages. There is nothing more to say about it.

Okay, you know better about this. Until now, it was not clear whether the current crisis qualifies as force majeure, but I haven't looked it up recently either. I will get advice from the lawyer.

At the moment, however, I don't see any efforts by the company to find alternatives. Basically, I am always in favor of joint solutions, but we are also reaching our limits; we are behind schedule (not only with the remaining trades; we were already behind with the shell construction), no signs of participating in running costs. And our private situation is unfortunately not so good either.
Oh, by the way, that reminds me of a not quite unimportant question.

We have to finance part of the construction costs with a loan, which will be due in the next few weeks. Until two weeks ago, that would have been no problem, but how are banks currently behaving when the regular income, let's say, is significantly reduced due to work stoppage? Have you heard anything about that?

We have to finance part of the construction costs through a loan, which will be arranged in the coming weeks.

You have started, or rather the GmbH has started, without the financing being secured?