They are the unused letter from the people's names when rearranged spell another related word, I have still two fireworks to get yet so can't help you out with the answer, i am struggling with the second one and also the 6th which i think is Pharaohs something but not sure what.
Just looking at this again is the answer not 7 letters long where as SPARKLER is 8, just wondering and does anyone know the answer to the 2nd firework, Thank you in advance.