Goalkeeper Longato is a product of the club's academy, and has re-joined the Tigers for this coming season.
Defender Hollins has previously featured at Colne and Southport.
Midfielder Palma, joins from Curzon Ashton on dual-registration terms in order to gain additional game time.
Manager Dave McGurk said: “Andy, or Trialist A as he’s been known has been with us all of pre-season. We wanted him in early doors but he was contracted with Colne. He’s got all the attributes to be a big player for us and I’m sure our fans will be happy to see him sign after his performances in pre-season.
“Darius comes in from Curzon and is a player I’ve always liked. He’s quick, direct and will provide us with more options at the top end of the pitch. He’s another one who will excite the fans.
“Riccardo is a brilliant lad and is going to be a top goalkeeper. His improvement under Chris has been plain to see. Craig may go out on dual registration and Riccardo will provide cover on match-days.”