In a related database at PoMS (but standing for People of Medieval Scotland instead of Paradox of Medieval Scotland) the entry from Malcolm MacHeth is slightly different. Perhaps more recent because it cites this article where the other does not:
"Malcolm Macheth, earl of Ross, was likely the son of Earl Aed (Heth, floruit 1128x1131). See Alasdair Ross, 'The Identity of the Prisoner at Roxburgh: Malcolm son of Alexander or Malcolm Macheth?', in Sharon Arbuthnot and Kaarina Hollo (eds), Fil Súil nGlais: A grey eye looks back. A Festschrift in Honour of Colm Ó Baoill (Ceann Drochaid, Brig o Turk, 2007), pp. 269-82."
http://db.poms.ac.uk/record/person/324/#
"Son of Aed the Earl" in a charter 1153-1160 of King Malcolm to Dunfermline, No citations to any other known relationships.
The dating notes say, "Death of King David I × consecration of Abbot Arnold of Kelso as bishop of St Andrews. Barrow claimed a date of 1157 × 1160 based on the notion that Malcolm MacHeth was the 'prisoner of Roxburgh', who is now generally accepted to have been Malcolm, an illegitimate son of King Alexander I."