It appears this has been lined up with three different spouses: Hawaise De Saint Amand, Aufricia/Aufrick Courci (of Man), and Isabel/Isobel. There is some error in this.
From what I've been able to research, Hawaise was actually the wife of Simon's son, also named Simon, second Lord of Montagu.
Secondly, Aufricia is found to be associated with Simon, but there's some doubt as to whether she was married to Simon. Moreover, even if she was married to Simon, she likely was not the mother of his children.
I've been attempting to fix this part of the tree as best as possible, but it's been a slow process as I have incomplete permissions over many of the related profiles. If anyone with more extensive permissions here wants to assist, chime in and let's see if we can iron things out.