husbands of Sibyl/Sybilla de Falaise Queen of Scotland

The Sibyl's certainly have varied birth dates. i would start by merging down to two - one who married de Belours, and one who married Alexander and see how it looks.

I have not studied these people or lines but: the most typical error of all is to assume that people with similar names are ONE person. Janet's suggestion is very good, and I would make a strong guess we're speaking of two different people. The reason for these mix-ups is of course that sources for women are fewer etc.

All the illegit children of Henry are also a documentation challenge, where (I guess) a lot of people have taken the opportunity to "claim" royal ancestry because of the ambiguous or missing sources.

Wikipedia now agrees with Medlands - marrying her to Alexander: http://en.wikipedia.org/wiki/Sybilla_de_Normandy

It also agrees with Medlands on her being the daughter of Sybil Corbet.

Neither Medlands or Wikipedia Show these two as her children, although they are presently on Geni as such; Mathilde de Coucy Aveline Ales de St-Hilaire

Medlands records another son of Alexander - Malcolm, by an unknown mistress. Is it possible Aveline & Mathilde are also the daughters of an unknown mistress?