The type of double pin stem in which a piece of wire is used both as
the pin stems and the hinge pin is generally a machine made product.
As you surmise it is difficult to bend the pin by hand close to the
ends of the charni?re.
There are a few ways to make a double pin. I like to bend the U shape
and then solder the center tube of a 3-part hinge to the base. You
should make a half-round groove in the base of the U to fit the
diameter of the charni?re. This makes for a stronger joint and a
much neater appearance. You want to use heavy walled tube, as
there’ll be a fair amount of lateral strain on it.
You can also take an L-shaped wire and solder it onto a standard pin
stem next to the hinge end.
After soldering work harden the wire by giving it a few twists.