I really appreciate you taking the time! I tried building a request similar to yours “count(Temples.Goshuin)”:
https://optimallanguage.backendless.app/api/data/City?loadRelations=Temples%2CTemples.Goshuin&property=Name&property=Temples&property=count(Temples)as%20TempleCount&property=count(Temples.Goshuin)as%20GoshuinCount&groupBy=objectId
But as a result it tells me:
Unable to execute query. Combining one-to-many relations (and/or relation depth) and named properties from one-to-many related tables produces an invalid query. Possible solution - choose either the entire relation column or named relation properties.