Illustrator printing a brochure

The problem might be related to printing them from Apple Preview, which is a basic application. It is better to print from a professional application such as Photoshop, for the reasons below.

When I open an image in Preview and choose File > Print, it allows Scale (by percentage) and Scale to Fit (where the print size depends on the printable area of the selected paper size). But nowhere does it tell you how large the document will actually print, in cm. It just wants to scale it to the paper size, or scale by percentage. But not by cm, so you are not sure what size you will actually get.

If you want to print from Preview at an exact size, before printing, it might work better to first choose Tools > Adjust Size. Set the Width to 30 cm, the other dimension should be adjusted proportionally, click OK, and then print that, and if the paper is large enough, see if the print comes out at the correct size.

“If the paper is large enough” is important here, because if you ask for a print 30 cm long, the very common A4 paper size is only 29.7cm long so it is not large enough to give you the print size you want. Hopefully you are using a printer that can take paper sizes large enough to reproduce any of the three print sizes you want.

Now, I have not actually tried printing from Preview, so that is sort of a guess. The reason I have not tried printing from Preview is because of the other potential solution for you which may be better: Print the image from an Adobe application instead. Unlike Apple Preview, printing an image from, for example, Adobe Photoshop lets you specify the exact print size.  Below, compare the Print dialog box in Photoshop to the one above from Preview. Notice that the Print dialog box in Photoshop does make it possible for you to specify an exact size in cm. This example is set up on an A3 paper size.

Remember, macOS lets you control what application opens a file when you double-click a file. For example, if you want PNG files to open in Photoshop (so you can print them more precisely),  change the macOS file association so that Photoshop opens PNG files instead of Preview.

I don't think I understand the sizes you want to print. Are they the same proportions as the size of the document?

So if they are all you need to do is calculate the percentage and then input that in the print dialog. I would export a PDF and print that through Acrobat.