I am not sure that matches up to the Peerage, but the way I read it, George Craufurd thought Dominus and Reginald to be one and the same, and thought he had two sons, Johannis and Hugo
Johannis, first son, had some unknown daughters and then he died in 1248 and was interred at Melross.
Hugo is the one who married the heiress from which comes the House Of Loudon, and George seems to have no doubt of that.