Royal Charter -- It's a village. If you do the first discard, you gain anothe one, but even though it's currently a $6 card, is it worthwhile? The card draw requires a discard first, which is actually a significant drawback. Your handsize after is the same as if you played a regular Village. It's good if you can discard a junk card to draw 2 better ones, but it's worse than Village if there's nothing you want to discard (in which case you either don't discard, or you discard a decent card and hope the two random ones are better). Overall, I don't think it's worth $6. $5, maybe.
But then there is the reaction. You need to word this differently. When you say "trash it", the last object you referred to is Royal Charter itself, so I was left wondering why I would ever bother using this reaction just to lose Royal Charter. I'm not sure if you can even use Royal Charter to trash all the cards that are discarded together, since some of the discarded cards would be covered up by other ones. I don't know. But yeah, the reaction as intended could bump it up to $6, sure.
Startled Horse -- the better comparison is Embassy, which is +5 cards, discard 3. This is just a small step down. This would already be very strong, but then you add in the option for early-game trashing. Too strong, I think. I'd modify it so it could be a mandatory trash, e.g. "Your opponent picks 3 cards; trash one and discard the rest".
Advertisers -- don't really know what to think of it. Discard-for-duration-effect is kind of a tracking issue (at the end of my turn, I may not remember whether I discarded for an advertiser or not) but it's not that bad. It has potential to spike a high cost card and it's good for when you want to Silver-flood. I don't know. I guess that means it's interesting.
Upper-Middle Class -- primarily serves as a village. The 1VP isn't enough to matter. As a village, it offers top-deck control similar to Scout, but it only draws more of itself. If you don't have any source of draw, this effect is actually a penalty more often than a benefit. If I only have two non-drawing terminals in hand, I'd prefer having a Necropolis because any UMC I draw is useless to me now and potentially helpful next turn. I guess it's fine, but if this and Village were both on the board I would prefer Village probably 90% of the time (the remaining 10% being for Silk Road and sometimes combos like Mystic and Wishing Well).