I haven't finished the game yet and I'm only past the first riddles so I can't explain the third but "It's yellow, blue, red and green! No one can reach it, not even the queen!" Is basically referring to a rainbow which has seven colors (there was a poster of a rainbow in the riddle room hinting to it)
And the Mrs Elizabeth Riddle is asking for how many dishes were saved (meaning plates) so there's still 5 dishes cuz they ate the food and left the plates!
I hope this helped if u were still confused :3