According to sources, Elena, daughter of Alexander Comyn, Earl of Buchan, married Sir WILLIAM of BRECHIN, SON of HENRY of BRECHIN, the illegitimate son of DAVID of Scotland, Earl of Huntingdon.
The Geni line contains an extra "Henry", which is in error and is messing up what should be an easy genealogical chart for the record.
Elena Comyn didn't marry Henry of Brechin (I'm not sure at this point who did marry him). She married his son, William of Brechin.
https://en.wikipedia.org/wiki/David,_Lord_of_Brechin#:~:text=Sir%20....
https://en.wikipedia.org/wiki/David,_Earl_of_Huntingdon
https://en.wikipedia.org/wiki/Alexander_Comyn,_Earl_of_Buchan
Here is William de Brechin and wife, Elena (or Helen) Comyn, in MedLands with all their noble ancestry laid out in fairly straightforward manner.
https://fmg.ac/Projects/MedLands/SCOTLAND.htm#WilliamBrechindied1292