

Q1: Can I trash just 1 specified card for the conditions of this card's Main effect?
No, you can't. A "by" condition can't be met if only some of the required actions are performed. The conditions for this Main effect require you to trash the specified number of cards.
Q2: There are 2 copies of this card in the battle area. Can I activate both of their Main effects and use one specified card with its cost reduced by the combined amount from both effects?
No, you can't. You can't simultaneously activate multiple effects that use a card.
Lv.4 NightChiropmon BT26-070 C Champion | Virus | Beastkin/Glowing Dawn/BEATBREAK [On Play] [When Digivolving] <Draw 1> and trash 1 card in your hand. [Main] [Once Per Turn] By trashing 2 bottom face-down cards from under any of your Tamers, you may use 1 Option card with the [Glowing Dawn] trait from your trash with the cost reduced by 2. --- <Retaliation> (When only this Digimon is deleted in battle, delete the Digimon it battled.)
Lv.4 NightChiropmon BT26-070 C Champion | Virus | Beastkin/Glowing Dawn/BEATBREAK [Digivolve] Lv.3 w/[Glowing Dawn] trait: Cost 2 [On Play] [When Digivolving] <Draw 1> and trash 1 card in your hand. [Main] [Once Per Turn] By trashing 2 bottom face-down cards from under any of your Tamers, you may use 1 Option card with the [Glowing Dawn] trait from your trash with the cost reduced by 2. --- <Retaliation> (When only this Digimon is deleted in battle, delete the Digimon it battled.)
Lv.4 NightChiropmon BT26-070 C champion | Virus | Beastkin/Glowing Dawn/BEATBREAK [Digivolve] Lv.3 w/[Glowing Dawn] trait: Cost 2 [On Play] [When Digivolving] <Draw 1> and trash 1 card in your hand. [Main] [Once Per Turn] By trashing 2 bottom face-down cards from under any of your Tamers, you may use 1 Option card with the [Glowing Dawn] trait from your trash with the cost reduced by 2. --- <Retaliation>
Lv.4 ナイトキロプモン BT26-070 C 成熟期 | ウィルス種 | 獣人型/グローイングドーン/ビートブレイク 【登場時】【進化時】≪1ドロー≫し、自分の手札1枚を破棄する。 【メイン】[ターン1回]自分のテイマーの下にある裏向きのカードを下から2枚破棄することで、自分のトラッシュから、特徴「グローイングドーン」を持つオプションカード1枚を支払うコスト-2で使用できる。 --- ≪道連れ≫(このデジモンだけがバトルで消滅したとき、バトルした相手のデジモンを消滅させる)