What area Justification-settings apply?

Hi @Jonathan32years , as Derek suggests Justification is a Paragraph and Paragraph Style property, so if you change the Justification setting from the Paragraph panel it would only apply to the selected paragraph(s). If the text in your 5 text frames have the same Paragraph Style applied the Justification for all the paragraphs could be changed via the style:

If you actually mean Vertical Justification as @James Gifford—NitroPress suggests, then you can select the text frames and apply the Vertical Justification via Object>Text Frame Options:

Set up a Paragraph Style, which can include justifications settings (and a whole lot more) and apply that to the text frames.

Under Text Frame Options (CTRL-B with the frame selected), if you set options on a Parent page text frame, they will apply to every page using that Primary Text Frame. If you select any text frame already in that document, the changes will apply only to those frames. You can (usually) select as many frames as you can see in your work area, even across pages.