Neutrons are not made of an electron, antineutrino and a proton.
However, you can get those out of a neutron through beta decay.
Neutrons are made of an up quark and 2 down quarks. The quarks
do have electrical charge (up = +2/3, down = -1/3. The third is
purely due to the long history of calling electrons -1 and
protons +1). Essentially, what happens is a down quark converts
to an up quark by emitting an electron and neutrino. You could
also do the opposite, known as inverse beta decay (this is
pretty difficult, if I recall, due to the rare neutrino
interaction. But I'm pretty sure this is how they detect
neutrinos). If you are asking what the force is that causes AM/M
annihilation, there is none. They are basically waves of
opposite amplitudes. So the electron is the crest and the
positron the trough. when they meet, they cancel each other out.
However, these are not virtual particles. They both have energy.
That energy has to go somewhere. E=mc^2, so something out of the
quantum foam gains positive energy