Fellow playmaker Rowan Milnes, back-rows Elliot Minchella and Matthew Storton plus young prop Anesu Mudoti have all signed three-year deals.
The deal - believed to be around £100,000 - will, at least, help cash-strapped Bradford pay off some of their creditors following their takeover earlier this week although it does leave their squad severely weakened.
As part of the agreement, however, 20-year-old Milnes - who starred in Bulls’ shock Challenge Cup win over Leeds Rhinos - will be loaned back to Bradford for the entire 2020 campaign.
He will then be part of the Rovers squad on a full-time basis from 2021.
KR say another of their player will also head in Bradford’s direction on a season-long loan next term.
Robins head coach Tony Smith said: “We are delighted to have these five players on board, and it was important that the deal benefited both clubs.
“To add young, ambitious and talented players is what we are striving to achieve and each of these signings are exactly that.
“The additions give us depth and choice in positions, which in turn gives us competition for places.
“To have people in form and playing well is an important part of our strategy for next year.
“Regardless of their experience, if they are doing their job, they are in consideration for the first team.
“They all see themselves as Super League players of the future and some have ambitions to go even further than that.
“They fit our recruitment remit and we are delighted to have each and every one of them on board at Hull KR.”
Keyes, 24, has Super League experience with London Broncos while Rhinos academy product Minchella, 23, made his top-flight debut for Leeds in 2013 before spending time with London and Sheffield Eagles before joining hometown Bradford.
Storton, 20, debuted for the Bulls two years ago but this was his breakout year, scoring four tries in 23 outings which helped him win the club’s Young Player of the Year award.
KR chief executive Mike Smith said: “We are happy to assist in Bradford’s preparations for the 2020 campaign, and the decision was made to loan Rowan Milnes back to the Bulls for next year to continue his development, whilst also loaning an existing Robins player,” Smith explained.
“The considerable fee involved, including loaning Milnes back to Bradford as well as one of our own players, shows that we are committed into helping Bradford remain sustainable in their ongoing rebuilding process.
“We all want to see a successful Bradford team and give them every chance of achieving their goals in 2020.”