Two jokers in the same meld
I have found no rule that prevent you from using two jokers in a single set:


  The Joker: There are two jokers in the game. Each joker can be used as
  any tile in a set, and its number and color are that of the tile
  needed to complete the set. On future turns, a joker can be retrieved
  from a set on the table by a player who can replace it during his/her
  turn with any tiles that can keep the set legitimate. This tile can
  come from the table or from a player’s rack. In the case of a group of
  three tiles, the joker can be replaced by a tile of either of the
  missing colors. When a player retrieves a joker, the joker will once
  again have any value or color. However, a player who retrieves a joker
  must play the joker on his/her current turn to make a new set, and
  must also use at least one tile from his/her rack on that turn (just
  as on any other turn). A player cannot retrieve a joker before s/he
  has played his/her initial meld.