The White Castle · Board game rules
How many clan meeples can be in one area?
Quick answer
It depends on the location: Training Yards and the Gates of the Castle hold unlimited Clan members from all clans, Gardens allow only one Gardener per clan per card, and the Daimyo's favor card and Castle rooms have limited, specific spaces.
Details
The Training Yards explicitly state that "Each Training Yard can house any number of Warriors from all the Clans," so there is no cap there [p.9 — Sending Clan Members to the Court of Himeji].
Similarly, the Gates of the Castle "can hold any number of Courtiers from all the Clans," meaning multiple players' Courtiers can stack up there without restriction [p.10 — Sending Clan Members to the Court of Himeji].
For Gardens, the rule is different: you can only place a Gardener on a Garden card "that does not already have a Gardener from your Clan," meaning each clan can only place one Gardener per card, but different clans can each have their own Gardener on the same card [p.10 — Sending Clan Members to the Court of Himeji].
The Daimyo's favor card (third floor) has a limited number of positions — if a Courtier reaches this level and there are no available spaces left, "you simply leave the Courtier in that room and do nothing more" [p.11 — Sending Clan Members to the Court of Himeji].
Watch out: Dice themselves follow a separate rule — only a single die can be stacked atop another, and only on spaces of the main board (not in a 1- or 2-player game at all) [p.5 — Stacking Dice]. This is distinct from the limits on Clan member pieces (Courtiers, Gardeners, Warriors) described above.