Two questions

First regarding edge battles; If a defender has no reserve cards, can they still declare defenders and just automatically lose the edge battle to prevent unopposed bonus and continue the conflict as usual?

Second regarding attacking; As an attacker I see that the defender has no available units to defend. So can I attack with one unit by itself that does no damage like C3PO just to get the unopposed bonus?

1) Yes. Even if you have no cards in hand, if you have ready units, you may choose them as defenders (or attackers) in an engagement. In part because of the situation you describe, in part because the Edge keyword exists. Having cards to place in an edge stack is not a requirement for the edge battle.

2) Yes, you may choose only a unit with no damage icons as an attacker. If you do, however, that unit must still focus to strike - its strike has no effect. If the engagement is not defended, you will inflict 1 damage to the objective for the unopposed bonus, as normal.

First regarding edge battles; If a defender has no reserve cards, can they still declare defenders and just automatically lose the edge battle to prevent unopposed bonus and continue the conflict as usual?

Note that the defender doesn't actually automatically lose... they win ties so the attacker has to have at least 1 force icon in their edge total to win. Sometimes you may block just to force the opponent to discard a card to turn on their edge dependent icons.

2) Yes, you may choose only a unit with no damage icons as an attacker. If you do, however, that unit must still focus to strike - its strike has no effect. If the engagement is not defended, you will inflict 1 damage to the objective for the unopposed bonus, as normal.

Nothing more satisfying than inflicting that 1 last damage on an opponent's objective when all their units are focused with an unopposed unit that usually doesn't do any damage, like Artoo Detoo or a Duty Officer .

I love swinging for unopposed with 3PO and lizards