Undo the updates for Google play store and services..those are pretty heavy..that right there will give you something to work with..
He may then get an "Update Google Play Services" error on some apps...
Try SD maid because there are things other than apps that can take your space (caches/thumbnails/duplicate files/other junk)...
Or follow these steps to eliminate such files:
- Settings >> Apps >> Reset App Preferences (For apps cache)
- File explorer >> sdcard/DCIM/.thumbnails delete this folder, it's gallery cache
If you download apps from places other than Play Store (SHAREit, APK Mirror etc.):
- File Explorer >> Search, type ".apk" (Without quotes) and delete all file that end with the .apk extention
Also, Goto Settings>> Storage and confirm if it is really the apps that are taking SD card space.
Also note that
some phones (actually I saw that on a tablet) will allow only a limited space for installing apps (that may be like, 1 GB of the 16 GB) and treat the rest of the space as another SD card. So there are 2 SD cards...