I'm a lowland Scot. It was "relations" in our family when I was a kid, and I still hear it from time to time. "Is he any relation to you?" is a common enough way of asking "Is he a relative of yours?" in Scotland.
"Relatives" seems to be taking over, though: our local hospital once had several rooms set aside near the intensive care unit and paediatric wards, labelled "Relative's Room". They've now moved the apostrophe to a more sensible place.

Grant Hutchison