iPhone - how to free up space when storage is completely full
If there are many apps installed from the Ap Store (or iTunes store) it may be possible to delete some of them to get enough extra space to be able to delete photos. After deleting photos any of the apps you deleted could then be reinstalled from their original store at no charge. (If this works, the only possible problem could be if any of the deleted apps aren't current since reinstalling them would bring in the current version which might work differently.)

If the problem with deleting photos is dependent on the app you are using to try to delete photos this may work; if it's a problem with lack of space for iOS itself then you'll probably just have the same problem trying to delete apps, too. It can't hurt to try. Hope this helps.