My TIFF files are placed on top of each other when imported to QGIS

To expand on @user30184 . The EXIF data stored in the image is the location of the GPS/camera at the time of image capture. There are several QGIS plugins that will allow you to map the locations of those points but the points will only be the locations of the camera at capture. These images will still not be georeferenced. These plugins typically allow you to click on the point in QGIS and see the image in an image viewer, but the top edge of the image will be relative to the top of the camera at capture and will not be rotated base on a compass bearing. The image will not be skewed based on the pitch, roll, and yawl of the camera at the time of capture.

Consider using WebODM (multi-platform FOSS4G), Agisoft Metashape (multi-platform), Pix4D (cloud), or DroneDeploy (cloud) - all with free trials - to generate an orthomosic image. These structure-from-motion (SFM) application will look at the EXIF data, and automate the stitching of the images to a single georeference orthomosaic. Some SFM packages will even output an NDVI image for you! Be warned, these are complicated software packages and require some experience and knowledge (despite what the drone companies will have you believe.)

These SFM software packages look for items in adjacent images and use those objects to paste the individual images together. If your images cover a large area of row crops, or forested lands - and contain no roads, buildings, water features, etc - the SFM software will not be able to stitch them together.