I have Robert's marriage to Alice Garrett down as 6/2/1724 not 1723?
Robert & Thomas had two North Side sales (67) to Thomas Casement and Robert Curghey in 1723. The first Thomas could be Robert's brother and possibily be the Kella conection.
If so then Robert's parents could be William Casement and Elizabeth Crowe. But as yet no documentary proof.
Other possible sisters, brothers
Elizabeth c 10/5/1686
Catherine c 29/6/1688
William b abt 1692
Margaret 24/10/1696
Thomas b abt 1697/98