As the title says, WI during the
Irish wars the scottish claimant to irish throne,
Edwad Bruce, acomplish gathering the support of the southern kings of Ireland, building a united front against the Anglo-Normans and bringing to reality
his brother dream of a Gaellic Alliance between Scotland and Ireland as counterweigh to England.
Well first of all Edward Bruce did have support of the Kings of Ulster for a while, and was in fact crowned High King. The Bruce's had had a real claim to the High Kingship (albeit a very distant one), so Edward could legally be King. However two things hampered his progress (and eventually killed him). One, he was to rash, before the Battle that he was killed in. He should have waited for Robert to arrive with fresh troops but instead lost his life.
The other problem is that the Irish viewed the Scots as invaders and so where willing to fight alongside the English to fight against the Scots and vice versa. Thus to get Edward to successfully stay as High King would mean that he was seen to be defending Irish interests and not Scottish ones.
However Robert Bruce in all likelyhood saw the Irish invasions as another way of distracting Edward II from invading Scotland, which of course worked.
So I think, in conclusion, it would not be enough for Edward Bruce to get the support of the South Irish Kings he would have to do something more drastic than that, as otherwise the Kings' support for him would ultimatly lessen and they would ultimatly turn against him.