Former Bradford Bulls player Peltier helped Doncaster RLFC reach the League One play-offs in 2021 while half-back Sweeting arrives from fellow Championship side Featherstone Rovers.
Outside back Greensmith spent time on loan at Doncaster from Wakefield Trinity last season but has opted to test himself at Championship level after an impressive stint in the third tier.
The 20-year-old made his only appearance for Wakerfield in July and said: “I am really pleased to be signing at Dewsbury and it was a straight-forward decision for me after speaking with
Lee about the club and his coaching techniques. I think my time at Doncaster helped me develop physically as I had only played academy level beforehand and it gave me the experience of playing in high pressure games, which is what is needed to perform at Dewsbury.
“I am looking forward to the new challenges that come with playing at Championship level.”
Explaining his decision to join the Rams, Sweeting said: “I am over the moon to sign with Dewsbury, they are a really good club and always do well in the Championship and I can’t wait to add to that. It was an easy decision for me to come on board.
"Lee Greenwood has brought the vision on to me of where he sees the club and what we can achieve next season and, hopefully, I can play a big part in that.”
On his move to Dewsbury, Peltier added: “A lot of people questioned my desire when I went to League One but I think it has shown that I went to a project where we tried to gain promotion but now I want to be able to answer the critics and show that I am a decent-level Championship forward that leads from the front.”