Riddle Number One
Martin's mother, Sayna,was slayed by Vilu Daskar, the evil pirate stoat in The Legend of Luke.
Luke was captured after surviving the Sayna's crash with the Goreleech(the red boat pictured on the book's cover.
After being captured, Vilu Daskar put Luke to work as a slave on his pirate boat.
After a while, Luke and some friends began a rebellion, in which Luke held Vilu to the front of the boat, while steering it straight into a rocky spire, giving his life, but taking Vilu's with him.

(A friendly old mouse said, "If you are searching for Luke he just left port on the Roaring.. Roaring... Roaring something [Roaringburn?]. I hope you catch up with him."
A grumpy shrew states, "Luke, that old goat hasn't shown his face around here for a while, last I saw of him he was heading to that mountain place [Salamandastron?].
A little dibbun said, "Luke's gonna be wid me fer supper [a Feast?]!")

Riddle Number Two
Slagar the Cruel took away five (or the answer to anagram no.5) Mattimeo.
Slagar, replace the g with a v is slavar (slaver) is what he was
Not his name, but the truth in the name, which is Chickenhound

Riddle Number Three
Arven, is raven scrambled up,
and if you read Mattimeo, you would have known the the mother of five (number five on the anagrams), Mattimeo's mother, Cornflower dressed up like the spirit of Martin, scaring the birds.
The red kite was a bird at Redwall named Stryke Red Kite, a large bird who killed the armies of General Ironbeak, and the general himself.