Offer for heating / sanitary / ventilation - is it realistic?

We took it out and instead come to about 26,000 with own labor + support for a "better" Weishaupt system as well as additionally 2x wall heating (2 bathrooms)

What do you mean by own labor here? Piping and installation yourselves? How do you handle the refrigerant of the air-to-water heat pump then?

Yes, even piping etc., with own labor are meant the simpler and helper tasks, by "support" I mean my brother-in-law, who is a heating technician and instructs or connects etc. But he does not do that completely "for free", it is included in the aforementioned...

By the way, I also find your offer rather expensive; you should definitely get more quotes... and to not give the heaters too much work, you give them the same or similar equipment... Have you already chosen the sanitary items? For example, we went to 3 suppliers and the prices there for visually similar equipment sometimes differed by +/- 10,000 euros. Your bathroom planner should actually help you avoid choosing "Porsche" everywhere, but unfortunately not everyone is capable of that. We paid about 65,000 (same equipment as you) but including 2 bathrooms with walk-in showers, wall heating in both bathrooms, and all sanitary ware (including bathroom cabinets).

I believe the variance in the equipment is too high to compare the sums like this. Therefore, it might be more comparable if you take that out. For example, what does bathroom furniture mean? Ikea Godmorgän (super good and cheap) or the ridiculously expensive stuff from Duravit, VuB, etc., which you can get more individually and cheaper from the carpenter. I received offers today; I can post them in detail tomorrow. But at first glance: from 60k to 90k (!) for heating, plumbing, ventilation, equipment all included. The identical equipment (since LV) is between 10k net and 14k net - wholesale 14k net. Reuter for comparison: €7,500 net (however, without installation).

...by "support" I mean my brother-in-law, who is a heating technician and instructs and connects etc.

You lucky devil, those are of course very favorable conditions where you can save a lot.

You really could faint here... we paid just under €30k for heating/plumbing including ceramics and furniture... simply for everything, 175m² underfloor heating, a total of 3 bathrooms, 2 showers - so it really blows my mind what prices are being asked here. Ventilation is still to come, but I have prepared it and so far it has cost €2.6k.