Rulings
Q1: Does "then, delete 1 of your opponent’s lowest level Digimon" in this card's On PlayWhen Digivolving effect activate even if my opponent doesn't have as many or more total Digimon and Tamers as me?
Yes, it activates.
Q2: I play this card when my opponent only has 1 EX1-073 Machinedramon in the battle area. At this time, I use "delete 1 of your opponent's highest level Digimon" in this card's On Play When Digivolving effect, and the 2nd All Turns effect on my opponent's EX1-073 Machinedramon interrupts it and prevents the deletion. If I then use this card's "delete 1 of your opponent's lowest level Digimon" effect, can the 2nd All Turns effect on my opponent's EX1-073 Machinedramon again interrupt the effect?
Yes, it can. The 2nd All Turns effect on EX1-073 Machinedramon can interrupt both deletions performed by this card's On Play When Digivolving effect.
Data Sources
Lv.6 Leviamon EX5-063 SR Mega | Virus | Demon Lord/Seven Great Demon Lords <Security A. +1> [On Play] [When Digivolving] If your opponent has as many or more total Digimon and Tamers as you, delete 1 of your opponent's highest level Digimon. Then, delete 1 of your opponent's lowest level Digimon. [All Turns] When an opponent's Digimon is deleted, gain 1 memory for each Digimon deleted.
Lv.6 Leviamon EX5-063 SR Mega | Virus | Demon Lord/Seven Great Demon Lords <Security A. +1> [On Play] [When Digivolving] If your opponent has as many or more total Digimon and Tamers as you, delete 1 of your opponent's highest level Digimon. Then, delete 1 of your opponent's lowest level Digimon. [All Turns] When an opponent's Digimon is deleted, gain 1 memory for each Digimon deleted.
Lv.6 Leviamon EX5-063 SR Mega | Virus | Demon Lord/Seven Great Demon Lords <Security A. +1> [On Play] [When Digivolving] If your opponent has as many or more total Digimon and Tamers as you, delete 1 of your opponent's highest level Digimon. Then, delete 1 of your opponent's lowest level Digimon. [All Turns] When an opponent's Digimon is deleted, gain 1 memory for each Digimon deleted.
Lv.6 リヴァイアモン EX5-063 SR 究極体 | ウィルス種 | 魔王型/七大魔王 ≪Sアタック+1≫ 【登場時】【進化時】相手のデジモンとテイマーの合計体数が自分のデジモンとテイマーの合計体数以上なら、最もLv.の高い相手のデジモン1体を消滅させる。その後、最もLv.の低い相手のデジモン1体を消滅させる。 【お互いのターン】相手のデジモンが消滅したとき、消滅したデジモン1体ごとに、メモリー+1。