Letter 1 1s from a cheating harlot. Prudie tells her she's a cheating harlot. I also tell her she's a cheating harlot. I would push the legal action angle: if you're gonna ruin your relationship with the current BF, you might as well take this creep down. (But does she have the written proof of the extorsion?)
Video letter is from a future cheating harlot. Prudie tells her not to cheat. So do I, as I observe that Prudie is pretty hot when she gets riled and self-righteous (and right).
It could be so much worse: Imagine this was the fruit of your loins
Letter 2 is from a woman who feels intellectually inferior to her brilliant son. Prudie says to stop worrying, and gives some OK advice on how to manage. I suggest reading the recent advice to the woman whose BF, family and friends are all so much more successful than her.
Letter 3 is from a woman whose husband wants to bring his 6-year-old from a previous marriage on their European honeymoon (Europe! Ooo la la!). Prudie says this is no honeymoon, and the inadequate mother/ex issue needs to be dealt with. I say, if you don't want the kid, you shouldn't have married the guy. But it's true this is no honeymoon.
Letter 4 is upset that a private matter involving their child was broadcast on Facebook by a well-meaning relative. Prudie says to nicely explain to relative that LW doesn't want her private business to be a subject of public knowledge. I say Facebook is the devil.