If you check your pictures you will notice that hoverflies (like all flies) have only two wings (bees and wasps have four).

Then, furthermore, I think one can recognize kind of a 'white spot' on the back/side of the flies in some of your pictures. These reduced wings are called "halteres". Please check this image.

The eyes of hoverflies are huge, their antennae very short, and their proboscis looks different than the one of bees.

Concerning #6 I just made the effort to determine the exact species for you: it's a female Eristalis arbustorum (please check for example the pattern on its back).