Replace floor joists and new floor

Good day to everyone first, we are new here and now have a problem with the ceiling or rather the floor in two rooms stacked on top of each other. We wanted to redo the ceiling and found out that the ceiling beams are eaten up by woodworm, so they need to be replaced. The floorboards upstairs were also in bad condition, so the entire ceiling with floor had to be completely exposed. The structural engineer told us to remove the old beams and replace them with glued laminated timber beams of the same thickness, take rafter spacing of 60 cm, and then either tongue-and-groove boards or OSB panels as flooring. So far so good. Now the installers who are supposed to install the glued laminated timber beams say they will not install them because the glued laminated timber beams are too thin and need to be 20 cm in height and 12 cm wide. The previous ones were 16x16 cm as solid wood, now glued laminated timber beams. Distance from wall to wall is 4.70 m, the rooms were previously fully furnished and inhabited. Now I don’t know what to do, the structural engineer told me again that it fits as it is and it is not technically possible to install larger ones.

Well, the structural engineer is really the measure of all things. He has to take responsibility for it. Why actually glued laminated timber? I always find solid wood better, but someone has to bear the costs after all.

The structural engineer specified the glulam beam, arguing that it is better in terms of load-bearing capacity and has fewer vibrations. Regarding the price, I couldn't really complain about the glulam beams; I paid €500 net for 16 pieces.

no one else there with an opinion

What kind of glued laminated timber beams did you buy? 16 pieces for 500€ at 16x16 would already be very cheap...

Regarding the topic otherwise, I can also imagine that the carpenters simply did not want to install your glued laminated timber beams. If you want to have such things done by the craftsman, you should also allow him to use his own materials. As for the dimensioning of the glued laminated timber beams, what the structural engineer says or has given in writing applies, he is liable for it, and thus it should be fine.

At the local timber merchant where we always buy, industrial quality not visible

the company wanted me to procure the material and only occasionally do the installation.
But I have the measurements from the structural engineer and the carpenter said that would be too thin, he wouldn't install those, they would have to be 20x20 then he would install them