The 34-year-old McKenzie spent seven years with Livingston and helped the club win Division Three this season.
Hyslop, 18, came through the youth ranks with hometown club Queens, moved to Scunthorpe United then joined Well in April.
The Dumfries-born goalkeeper, who was first involved with the Division One club as a 14-year-old, recalled that he was invited back to Palmerston by the club's youth coach and former captain.
I don't just want to be just a spectator
Queen of the South goalkeeper Ross Hyslop
"On leaving Motherwell at the end of last season, I was asked by Jim Thomson to play a few games for the Under-19s," Hyslop told Queens' website.
"But, sod's law, I broke my leg in three places and finished up in hospital. It was a real sickener.
"However, I've now signed a one-year contract with my hometown team and I want to be right in there challenging David Hutton and new man Roddy McKenzie.
"I don't just want to be just a spectator."
Hyslop has yet to make his senior debut despite being named on Queens' bench against Dundee while aged 15.
Being a spectator as an unused substitute against Celtic was as close as he came to making his debut for Motherwell in the Scottish Premier League.
McKenzie, who has also signed a one-year deal, is at the other end of the experience scale, having made more than 250 senior appearances.
The goalkeeper began his career with Hearts and also played for Dunfermline Athletic in between two spells at Almondvale, the latest of which began in 2008.
Livi have already signed 39-year-old goalkeeper Tony Bullock, who was released by First Division club Dundee, this summer.
Source: BBC Sport
Source: BBC Sport