In regard to the second of your two bullet points, I don't recall Strange saying that a person had to've died in battle with Spider-Man in order to be transported by the spell.
The eventual death of the villains is a key element of the plot. Spider-Man 3.0 and the five villains assumed that the villains were transported to the MCU just before they died while fighting Spider-Man in their respective realities. Doctor Strange neither confirmed nor denied it. His only goal was to stop the chaos that the misfired spell had caused. Actually, if Sandman & the Lizard had guessed the truth, they would have sided with Doctor Strange against the other villains.
It is not a plot hole but, in my view, in term of coherence, it is far from being one of the highlights of the story.
In regard to your first bullet point, it's not explicit, but there are implied explanations for both of those (though in the case of Venom 2.0, it involves spoilers for Venom: Let There Be Carnage).
Many thanks for your thoughtful analysis.
My reaction is the same in this case: These implied explanations are far-fetched and far from being highlights of the story.
The truth is that things happened because they served the purpose: Sony & Marvel Studios wanted to make a crossover film with the 5 main villains of the previous film series and the Spider-Man of the MCU.
Since I enjoyed the movie, it's ok in my book.
The interpretations I've seen (bot being a stretch, but acceptable since the film was enjoyable)
The Lizard persona died when Spidey 2.0 cured him in his movie, he was transported right before that.
Sandman was in his sand form and kinda patchy throughout, the theory I've seen is he was transported from some later date before he lost all coherence and collapsed into a pile of sand.
Loved the film, so they work for me.
Other option, they are from slightly different universes from the movies we saw where they did die.