Q1: Can the condition for this card's All Your Turns effect be to return only two cards from your trash to the deck?
No, you cannot. The conditions of the By effect cannot be performed only in part. For the conditions of this All Your Turns effect, you must return the specified number of cards from your trash to the deck.
Lv.7 DeathXmon BT20-082 SR Mega | Virus | Unanalyzable/X Program <Security A. +1> <Reboot> <Blocker> [All Turns] When this Digimon would leave the battle area by effects, by returning 3 cards with [Dex] or [DeathX] in their names from your trash to the bottom of the deck, it doesn't leave. [End of All Turns] [Once Per Turn] Delete all Digimon with the lowest level.
Lv.7 DeathXmon BT20-082 SR Mega | Virus | Unanalyzable/X Program <Security A. +1> <Reboot> <Blocker> [All Turns] When this Digimon would leave the battle area by effects, by returning 3 cards with [Dex] or [DeathX] in their names from your trash to the bottom of the deck, it doesn't leave. [End of All Turns] [Once Per Turn] Delete all Digimon with the lowest level.
Lv.7 デクスモン BT20-082 SR 究極体 | ウィルス種 | 解析不能/Xプログラム ≪Sアタック+1≫≪再起動≫≪ブロッカー≫ 【お互いのターン】このデジモンが効果でバトルエリアを離れるとき、自分のトラッシュから、名称に「デクス」を含むカード3枚をデッキの下に戻すことで、離れない。 【お互いのターン終了時】[ターンに1回]最もLv.の低いデジモン全てを消滅させる。