Can I put more than one Master Builder in the King's Court?
After taking another pass through the rules, I see no reason this would be forbidden.  That being said, I see no case where this would be a good play.  You gain nothing by placing a second builder here, and at best you are causing one player to pay taxes.  I suppose in the very narrow situation where 1) this is the last space (and therefore you know which player will have to pay), 2) you know the player who will have to pay will not be able to afford it and therefore lose victory points, 3) that player is in first place, and 4) you are in second place that this play could be worthwhile.  However, even in this case it seems likely that the player targeted could make up the one or two points they would lose (two to five divided by two, rounded down) with the action they choose instead.  I think it is always going to be preferable to take another action instead.