Nicholson 25 is a vastly experienced and well respected front row forward who is a former Leeds Rhinos junior and has also had spells at York City Knights, Featherstone Rovers and most recently Doncaster.
Roberts 24 is a half-back who was recently on trial at York City Knights and was previously with Sheffield Eagles for three years.
Walker 20 is a utility back who scored a try as a trialist on his debut in the defeat at Oxford before sustaining a knee injury and is currently undergoing rehabilitation.
Head coach Gary Thornton said: “I’m delighted to have Matty on board. I’ve worked with him previously at both York and Doncaster, and he is a quality player and a quality individual.
“He has had a horrendous time with injuries which has hampered the progress of his career, but he is good to go now having fully recovered from his latest injury, and is looking forward to pulling on the Hunslet jersey.
“To have him on board for the rest of the season will be a massive boost to us. He is very professional and will bring a fantastic attitude and experience to the group.”
Thornton added: “I’m really pleased to bring Shaun to the club.
“He is a talented half-back, tough defender with a great kicking game and organisational skills.
“Shaun hails from Doncaster, having played for both Moorends and Toll Bar, and was on my radar whilst I was coaching Doncaster, being recommended by the backroom coaching staff there.
“He spent three seasons at Sheffield Eagles, but wasn’t able to force his way into the first team due to the presence of quality half backs like Kyle Briggs and Dom Brambani, but he will be a fantastic addition to our squad.
Meanwhile hooker Matthew Tebb has been released to allow him to return back to Shaw Cross Sharks.