It is possible that the Bissetts aided de Lacy against his Scottish rival Donnchad, Earl of Carrick and received some of the latter's lands for their assistance, but while attractive no account of such a thing is preserved. Following de Lacy's death, Brian Ua Néill rose to become the most powerful king in all the north of Ireland and in the 1250s was busy smashing the young earldom to pieces, killing many of the English (presumably Scots also) and destroying their castles, and the Bissetts may have been among the sufferers. However, the report of John Byset's death in 1257 shows that the family were viable and may have found themselves possibly even the most prominent British family remaining in Ulidia for a period, since no others are mentioned in the annals. O'Neill was elected High King of Ireland in 1258 by the O'Conors and O'Briens but his death only two years later in the Battle of Druim Dearg came too soon for a major Gaelic overlordship to be established and Walter de Burgh, the Lord of Connacht, was created Earl of Ulster four years after the conflict to preserve England's interests there. Possibly the Bissetts were forced to become his subordinates, but it has been argued that theirs was understood to be, in any case, a palatine lordship from its creation, whenever that may have been. The historian Archie Duncan has suggested that Edward Bruce may have spent some time as a youth with the Bissetts, and it was to Rathlin Castle that Robert the Bruce and his followers retired in 1305/6 after suffering losses in Scotland. Despite the decrees of Edward I of England, they were reportedly welcomed by the owner Sir Hugh Byset, usually presumed to be a son of the Mac Eoin, and at this time Rathlin Island belonged to the Lordship of the Glens. It was also here that Robert Bruce may have begun planning to re-conquer Scotland, and later Sir Hugh's manor of Glenarm is where his brother Edward arrived after their victory in the Battle of Bannockburn. Parliament sent summonses to a total of five Byset magnates when hearing news of the invasion, their names being John, Hubert, William, and two named Hugh, one presumably Sir Hugh Byset, and the John Byset possibly being the Mac Eoin gone into rebellion to fight on the side of the Scots (for whom see below).