How to keep all the images in the document in the same size and exact places in Adobe Frame Maker?

It is a very open question. If your images reside in anchored frames, the frame + the images in the frames are going to float with the text flow. Add more text prior to the position of the anchor and your frame will float along with the position of the anchor. This is a good thing, if the thinking behind the image, is that it refers to specific content in the text.

You can also insert images which are not anchored in the text flow. When you add or subtract text, the image stays where you put it on the page. In that instance the thinking may be, that the image will refer to the text on a, perhaps, broader level or that it is there for decorative reasons. Or something entirely else 🙂

@Jeff_Coatsworth is right, though. If you want absolute control - use object styles!

Think that's covered by Object Styles - https://help.adobe.com/en_US/framemaker/using/using-framemaker/user-guide/frm_graphics_gr-topic_graphics-object-styles.html