The Thanos Imperative/Headscratchers

• Why, to get Death close enough to Mar Vell, did Thanos have to be killed in that ritual place. Wouldn't Death have been summoned the moment Mar Vell killed anyone in the regular universe?
• Did Thanos not exist in the Cancerverse ever? How did that happen?
• How did Cancerverse Captain Marvel kill Death? Has Captain Marvel always been that powerful?
• Why did the Many-angled ones need Death to invade?
• What happened to anyone who gets obliterated in the Cancerverse if they cannot die?
• How did the Scarlet Witch hold off the Man-angled ones when the other magic users couldn't? Weren't all the Avengers turned at once?