Construction company halts work despite overpayment

Have you considered filing a criminal complaint for fraud? This is against a person and not against a GmbH and is also not protected by "insolvency". In addition, "public interest" arises. You mentioned that there may be other affected parties. Find them, that would support a criminal complaint. What is to become of your house - sorry, I have no advice on that either. There are fraudsters who know their craft and even the most cautious can be affected. What you learn from it is a private matter. Don’t let anyone convince you otherwise.

The insolvency is so far only a suspicion, but it is very likely because he 1. tells third parties himself and 2. has had a second construction company registered in his name for a month. I would also like to know the answer to the second question.

The insolvency is so far only a suspicion, but it is very likely because 1. he himself says so to third parties and 2. for a month now there has been a second construction company registered under his name. I would also like to know the answer to the second question.

My developer is (still) reputable and in business. He has founded his own GmbH for every 2-3 houses. This seems normal for some. They then only have liability of 25k.

I wanted to file a criminal complaint, but on the urgent advice of my lawyer, I did not do so. HE says I must not do anything now that could jeopardize the settlement. Although the settlement negotiations have been dragging on for over 3 months and I no longer believe in a conclusion. This person is the GmbH!!! He is the site manager and only works with subs.

That is still my great hope. It is said to be the last to die.

Does your lawyer know that insolvency might be looming? The reasoning behind the approach does not read that way. In that regard, perhaps more can still be found out.

Unfortunately, I can't give you any solid advice either, except to look forward and no longer look back.
Your lawyer apparently sees it differently.