The fresh deals will see the pair remain contracted at the club until the end of the 2018-19 campaign.
Manager Stuart McCall said: “Prior to the closure of the summer transfer window, there was actually some interest in Killa from abroad.
“It would have been a big offer for him in terms of finances, but Matt wanted to stay.
“The way he has been playing this season and the loyalty he has shown to the club, Matt deserves his contract.
“He is a good influence in the dressing room as is Nat.
“He (Knight-Percival) had shown his adaptability to play on the right-hand side of defence despite being left-footed and has been defensively sound again in the early stages of this season.
“ He is a great professional and very committed to the club.”