Yes, as long as they are different sources, then they stack. In other words you can't stack two different crown store scrolls, like one at 50% and one at 100%.

But, Ambrosia plus Scroll, yes.

Same with the Event, and Ambrosia, or the Event and the Scroll. What I have not tried is the Ambrosia, a Scroll and the Event, but I don't see why that would not work.

In case your wondering, the Jester Event tomorrow has a pie that doubles exp gained for 2 hours.