Was there any fallout from the $20 gift?
It sounds like you're going to get grief no matter what, because these people are ehell bent on taking the most uncharitable view of everybody's actions. If it makes you feel better, their toxic behavior probably makes them far more miserable than any grief that they might be giving you. What a sad life, to work yourself into a tizzy about stuff like this.
Me, personally, I would send $200. Because that's what I would have done for any wedding where the relatives weren't crazy. That way, I wouldn't fall into the trap of attempting to second-guess crazy people.
In other words, never go against a Sicilian when death is on the line. :p You can twist your brain into knots, trying to figure how they're going to view your wedding gifts... but the truth of the matter is, they're probably going to take a negative attitude about it no matter what. So, do what you'd do if you were dealing with people who aren't nutters. Don't play their game.