You certainly seem eager to dive in, or rather, you seem to really thrive in contract law (at the same time, however, like with the tiles, due to the history and time pressure, making avoidable mistakes).
From an outside perspective and without emotions: if problems repeatedly occur at many interfaces (window sealing, screed heights, etc., etc.), you should still admit that your expertise is not enough. And with that, I would also be very critical of a sole individual contract award, since every trade could blame missing planning or errors in previous work.
Although you unfortunately regularly have problems with construction consultants and general contractors/companies and subsequently time- and nerve-wracking trouble, I would personally still consider starting everything over from scratch.
Organize financing, wait for court decisions regarding funds, take a breather, and then calmly and strengthened look for one or more reliable partners (they do exist, I hope regional ones are not already all alienated or warned), work out the planning details of the outstanding trades, and then finally bring the whole thing to an orderly conclusion. Because: how much is your time worth to you, and how much are your nerves worth?
And then at some point carry out the construction as a cooperation rather than, as has often been the case so far after a short time, as an adversarial process! Also, don’t forget what it was originally about in my opinion: a house for your children. How do they actually feel about the whole thing? From your description, it currently seems more like a one-woman show. Is the supposed bargain really worth it to you? Or could you, even though you spend more than originally planned over the next 30 years, live contentedly? Happy kids, happy life?