Host, who has played 52 NRL games from the Dragons, has been signed until the end of the 2023 season.
Mlne, who has made 19 NRL appearances for the Dragons and Warriors, has been locked in until the end of 2022.
Rabbitohs Head of Football Mark Ellison was excited to announce the pair’s signatures.
“We’re really looking forward to Jacob and Taane joining us next season,” Ellison told rabbitohs.com.au.
“Jacob comes highly recommended by JD (Demetriou) and he has been on our radar for a number of seasons.
“He has performed strongly for the Dragons in the opportunities he’s been given and we’re looking forward to him pushing for a spot in our top 17 on a weekly basis.
“Taane has had limited opportunities to impress in the NRL, but when he has been given a shot, he has shown he has what it takes to perform consistently well at the top level.
“We’re looking forward to having them join our squad for the 2021 pre-season and seeing what they can achieve under the guidance of Wayne (Bennett) and ‘JD’.”