Kidnapped and no allies
The way I read Kidnapped is that you make the skill test regardless of whether you have allies or not. If you pass then nothing happens. If you fail then one of your allies is Kidnapped. If you fail and have no allies then you take 2 damage.
There is apparently a ruling somewhere that says this. (See https://arkhamdb.com/card/02220)
Where Doom Awaits and Hideous Abominations
If "the investigators put Silas Bishop out of his misery" then you use the Hideous Abominations encounter set. Otherwise it is unused and will stay where ever you keep all the rest of your cards.
See "Drawing Cards" in the rule reference. When you need to draw a card from your investigator deck and cannot because it is empty. You first shuffle your discard pile to make a new deck and then take 1 horror.
Also yes, you would take 20 damage. Sucks but the second one probably never got drawn since the first one likely defeated you.