sgillinn = a shilling (old denomination)?
Not sure if they're cognates to be honest. The Gaelic for shilling is 'tastan'.
They are definitely cognates!
Then we must agree to disagree!
Two pence is one way of saying it but tuppence is a perfectly legitimate alternative.
Perhaps in English, but I wouldn't consider it an acceptable translation of dà sgillinn.
Most people I know say two p. Tuppence is old-fashioned and mostly from pre-decimal days, or people who watch Mary Poppins.