1:
Hippodrome/Fighting Fantasy may be it.
2:
Knights of the Round is my first choice. I'm going to assume it's not one of the obvious choices like the D&D capcom games or Golden Axe, so Knights of the Round is one of the common options.
King of Dragons is another, also a capcom game so it saw widespread placement in many arcades. The hurdle i'm running into is the fighting your friend at the end. I can only think of double dragon as doing that. Do you happen to remember if it was 2d or 3d? Side on view, top down, or isometric?
3:
Ninja Commando is my best guess for the vertical shmup category.
Do you happen to remember the year you saw it? Mounted gun games sort of disappeared between the late 90s and early 2010s so it'd help to know if i'm looking for something more recent. Gunblade NY/machineguns LA are about the only games I can think of that even involve people on the street, but neither have anything resembling monsters or skeletons.
Freaky Flyers was on PS2/xbox/gamecube, shipped out demo discs for ps2 and xbox, and seems to tick the boxes. The level you're thinking of might be "coyote canyon" (8:00 in the video).