I've previously listed William and his siblings. In the light of the rules for given names I discussed in the last post, I'm going to revise that slightly.
If Sampson were the second son, he would have been named after his maternal grandfather. This makes a certain amount of sense, since his name is unique among the Harbisons to himself and his descendants. That would then made John the third son, named after his father. It is notable that the first sons of most if not all of William's siblings were also named John. So this tends to bolster the hitherto rather weakly-proven conjecture that William's father was the Catholic John Harbison resident in Ballyneill during the 1766 religious census.
The fourth son would then appear to be Henry. He would have been named after his grandfather William's eldest brother. And, sure enough, the two Harbisons mentioned in the Protestant Householders census of 1740 for the parish of Ardtrea in the barony of Loughinsholin are William and Henry! There is an entry in the will index at PRONI for Henry Harbison, d. 1765, so he never made it to the religious census. It is also possible that William and Henry were Catholics, since Bill Macafee noticed that apparently the census for Loughinsholin seemed to include some Catholics. Or William Harbison in the 1740 Householders List may have been the legendary Wild Billy Harbison.
Wild Billy Harbison married a Catholic servant girl-- Like dolmens round my childhood, the old people, from Poisoned Lands, and other poems, John Montague, 1961. In all honesty, I'd have to admit I have no clue about the birth order of the final three sons, though I suspect Edward was the youngest. Likewise about the three daughters, although, I suspect, Eleanor was the third.
When all his Loyal family passed on:
We danced round him shouting 'To Hell with King Billy'
And dodged from the arc of his flailing blackthorn
Forsaken by both creeds, he showed little concern
Until the Orange drums banged past in the summer
And bowler and sash aggressively shone