Prop Adam Walker will leave Hull KR, but Thomas Minns will remain at Craven Park after pledging his future to the club.
Minns, who had two years left to run on his contract, was the club's top try-scorer last season and will take his place in Hull head coach Tim Sheens' squad for the 2017 season.
Head of rugby Jamie Peacock said: "Thomas will be a tremendous asset for us in the Championship having really excelled in the competition a couple of years ago and it was important that we retained a quality young player such as him.
"He's still only 22 and has plenty of development ahead of him, but he's got tremendous experience for his age and really showed what he could do last season with regular game time.
"He certainly knows where the try line is and he proved what sort of impact he can have against Super League opposition so we're delighted to retain his services for 2017 and beyond."
On Walker, Hull KR chairman Neil Hudgell added: "I can't blame any player for wanting to play in Super League, but in my opinion Adam is a special case and we felt he owed us a year for the support the club has given him. Instead, he was the first to head for the hills.
"It was us who sat round the table with his legal team and repeatedly defended him in the face of criticism.
"By contrast, his agent has crawled out from under his stone at the smell of cash to take his slice. It's a great disappointment for the club to lose Adam but we will move on."