At the end of the game, I replaced a joker with a tile, then used that joker with another joker and a 10 tile to make a run of 10,11,12 to win. Is this a legitimate play?
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.
According to these tournament rules, two jokers in one meld is a legal move.
Either joker can be used to complete any Meld (either Set or Run). Two jokers can be used in a single Meld.
It would depend on the rules set you're using. Most rules do not prohibit it (and therefore allow it by consequence of the rest of the rules).
According to the "Variations" section of the Rummikub rules on Pagat:
Most rule sets do not explicitly state whether two jokers can be used in the same combination. It would be unusual to want to commit both jokers in this way, but since there is no rule against it, it is reasonable to assume that it is allowed. Indeed the current edition of the online rules from Lemada Light Industries Ltd. does explicitly allow it. A player who puts down a combination of a three tiles of which two are jokers must clearly state whether it is meant to be a set of equal tiles or a sequence, and this will determine the tiles that are needed if a player later wants to reclaim a joker from this combination.