Do Seismic Charges or Proximity Mines get any rerolls for damage? Like with focus, target lock, marksmen or anything that can change dice? Or do they not count as "attacks"?

I would say no on both counts. The seismic charge simply deals one damage with no rolls. The proximity mine rolls does but it is not an attack, the defender doesn't get to try and evade and even if it were an attack, the mine does not have any focus tokens or target locks as it is the mine doing the attacking.

I also think no on both accounts. Essentially proximity mines are like asteroids, but they hit harder (3 dice instead of 1) and go away once they are detonated. Seismic charges just deal 1 damage to every ship within range 1 at the end of the activation phase. So no dice are even rolled for them at all. No tokens can be used to strengthen or reduce the effects of these weapons.