According to Alan Ford and John McCafferty (The origins of sectarianism in early modern Ireland), Robert was born in Kent. He married Maud Golding, and does not appear to have left Ireland after 1547. There is no evidence of him having a son named William. His known sons are James J'ans (mayor of Dublin in 1593) who had 3 wives (including Catherine Cusack, daughter of the mayor of Dublin), and Thomas J'ans who married the daughter of Captain William Piers, a favourite of Queen Elizabeth.
Janes, or Janns (James Janes, Mayor of Dublin, 1593, son of Robert Janes, or Janns, Master of the Ordnance in Ireland, 1559. Visit. city of Dublin, 1607). Gu. on a bend ar. three Cornish choughs sa. beaked and legged of the first.>
Robert did have descendants in Devon and Cornwall, but not until several generations later (Thomas J'ans who died circa 1759 eventually settled in Bideford and one of his grandsons, Wrey J'ans (1737-1816) was based in Cornwall.
There does not appear to be any connection to the Imes family.