Attack-minded Ephraim joins the Robins from QPR on a deal until the end of the season, while defender Amougou moves to Ashton Gate from Burnley until April 21.
Israeli defender Keinan arrives from Cardiff the the remainder of the campaign after failing to break into the Bluebirds' first team in 2011/12.
Ephraim has also struggled for first-team chances at Loftus Road this season, turning out just three times for his parent club, and the 23-year-old enjoyed a spell at Charlton earlier in the campaign.
Amougou, who is out of contract with the Clarets in the summer, has made 17 appearances for Burnley this term but has not featured for the Lancashire outfit since the 4-1 defeat at Norwich in the third round of the FA Cup in January.
All three players could make their City debuts against Middlesbrough at the Riverside Stadium on Saturday.