Storkules saying that Donald and Daisy being on a second date means that they are married is a reference to wedded life in mythological Greece. As in, you just pick the lady of your choosing to be your wife after one or two nights together; no relationship building needed.
Aside from abusing his godly powers to the point that it made the other gods dethrone Zeus, they also have ample reason to not want him to be their leader: Zeus preventing them from fighting during "Moonvasion" nearly cost them their worshippers and domains with the near-destruction of the mortal realm.
Why do the Titan's victims survive getting eaten? Because there's a precedent to this in Greek mythology: Zeus' siblings all get eaten by their father Cronus, but after Zeus defeats Cronus, he can retrieve all of his siblings unharmed.
Storkules doesn't feel that Donald and Daisy's love interferes with his love for Donald because they are different forms of love according to the Greek concept of The Four Loves: the eros between Donald and Daisy is different from the philia between Storkules and Donald.
Della may not know it, but Penumbra reminding her of Donald really isn’t far off here. What Donald went through with Storkules is almost the same thing Penumbra did with Della when they were roommates: Both Storkules and Della acted very chummy and rambunctious towards Donald/Penny, not realizing how their antics, though well-meaning, were annoying and unwarranted.
Why doesn’t Della accept the offer to take Zeus’ place apart from just trying to raise the kids’ self-esteem even though she is fairly responsible enough? The same reason she wouldn’t want to take over her uncle’s company when he retires; it’s just too big a responsibility for her, and she already knows that this isn’t her calling.
In the Iliad the gods once tried to dethrone Zeus and failed, but here they succeed and strip him of his powers. There's two big differences between the mythical attempt and the one in the show:
In the Iliad not all the gods are on it (it's openly stated that Thetis and Briareus kept the other gods from binding Zeus, allowing him to beat them down), but here they're all on it.
As Homer doesn't include Heracles as a god, he didn't take part in the coup. Here, however, Storkules is a god, and took part in it.
Given the obvious amount of Ho Yay that Storkules feels toward Donald, why is he not jealous of Daisy? Because, in-universe, Storkules considers himself, Donald, and Daisy to be a One True Threesome. Whether his feelings for Donald are eros or philia, he doesn't consider her a rival for Donald's affections, so much as an addition to their relationship.
Della's speech to Scrooge about the kids constantly feeling the need to prove themselves likely comes from experience—since she and Donald have been accompanying (and possibly living with) Scrooge for at least twenty years, ever since they were the same age as the triplets. As seen in The First Adventure!, Scrooge was already a seasoned adventurer who didn't want children hanging around him when Donald and Della showed up, so Della likely faced similar issues during her own "kid sidekick" days with Scrooge.
Della's encouraging the kids not to let their mistakes and shortcomings drag them down and reading the riot act to her uncle is a subtle revisit to what she went through with Louie in the events between "Timephoon!" and "Richest Duck In The World!". Scrooge getting worked up with the kids' botching up the mission and insensitively implying he would replace them isn't unlike how Della, even if discipline was necessary in Louie's case, constantly put him down to the point where she made prerecorded lectures that sounded as if she had it out for him. The common denominator in both cases was how those on the receiving end weren't given enough of an opportunity or drive to grow in a constructive way. Della now understands that mistakes and flaws are inevitable, but at the end of the day, it's important to allow kids room to grow. Once Scrooge apologizes to the kids for letting their failures get the best of him, they regain the will to learn from their mistakes and try again. It’s for that reason Louie was able to learn his lesson as he (without realizing it) was given the opportunity to confront his worst flaws and deconstruct his way of thinking that contributed to said flaws, and without Della's involvement.
