Alice clearly did marry Roger, and was the mother of his son and heir, Ralph, as shown by the evidence below. The date of "before 1255" for Roger's marriage to Isabel, which is based on the belief that she was Ralph's mother, is therefore also incorrect.
The marriage contract referred to above is printed in The Beauchamp Cartulary Charters 1100-1268, ed E. Mason, p.214 (1980), together with a grant by Humphrey de Bohun to Roger de Tosny, of the manors of Newton (Tony) and (East) Coulston, Wiltshire, in marriage with his daughter Alice (p.216). The manors were given in free marriage to be held by Roger and his heirs by Alice, and were to revert to Humphrey if Alice died without issue. This grant is dated by Mason to probably c.1251, when Roger reached the age of 14.
The previous grant to Queen Eleanor on 26 April 1242, referred to by Complete Peerage, was in fact a grant of the lands only, not of the marriage and land...; it is referred to again as a grant of the lands in a subsequent grant of scutage to Queen Eleanor, on 3 May [Cal. Close Rolls, 1237-42, p.422]. (A later order, dated 12 February 1243/4, does refer to the lands and the marriage of the heir having been granted to the queen, but this is presumably an error [Cal. Close Rolls, 1242-47, p.158].)
The manor of Newton Tony descended to Roger's son Ralph (d.1295) and then to his son Robert [Victoria County History, Wiltshire, vol.15, p.146]. East Coulston passed to Walter de Beauchamp, who married Roger's daughter Alice, and later to their descendants [Victoria County History, Wiltshire, vol.8, p.235].