Based on how Indonesia bonus, looks like you just need to add in a piece within the ModifierArgument table to require 2 tiles instead of using the default 1 tile.
Code:
<ModifierArguments>
...
<Row>
<ModifierId>TRAIT_NUSANTARA_COAST_HOLY_SITE</ModifierId>
<Name>DistrictType</Name>
<Value>DISTRICT_HOLY_SITE</Value>
</Row>
<Row>
<ModifierId>TRAIT_NUSANTARA_COAST_HOLY_SITE</ModifierId>
<Name>TerrainType</Name>
<Value>TERRAIN_COAST</Value>
</Row>
<Row>
<ModifierId>TRAIT_NUSANTARA_COAST_HOLY_SITE</ModifierId>
<Name>YieldType</Name>
<Value>YIELD_FAITH</Value>
</Row>
<Row>
<ModifierId>TRAIT_NUSANTARA_COAST_HOLY_SITE</ModifierId>
<Name>Amount</Name>
<Value>1</Value>
</Row>
<Row>
<ModifierId>TRAIT_NUSANTARA_COAST_HOLY_SITE</ModifierId>
<Name>TilesRequired</Name>
<Value>2</Value>
</Row>
...
</ModifierArguments>
So in your mod, you should just need to add the following section to apply that to the Dance of the Aurora belief so that 2 tiles are required.
Code:
<ModifierArguments>
...
<Row>
<ModifierId>DANCE_OF_THE_AURORA_FAITHTUNDRAADJACENCY</ModifierId>
<Name>TilesRequired</Name>
<Value>2</Value>
</Row>
...
</ModifierArguments>