When using role terms, I would say something like, "partners are across from you, neighbors are up and down from you, larks are on this (indicate) diagonal and robins are on this (indicate) diagonal.
If using ECD-style positional calling, I might use first and second corners, but would hasten to distinguish between the persons and positions.
As Angela said, I do not use a generic collective term for them because there are few, if any, dances where such a relationship description is necessary. For a proper dance, I would identify neighbors as on the diagonal, and would probably refer to "robins' side and larks' side" of the set.