Knights were allowed to marry their sisters? Seems so: Agnes de Houghton
Either that or there's confusion here about Hocton and Houghton. Or Lancashire was experiencing bad weather or drought of some kind in the early 13th Century, it's probably in the history books somewhere.
It appears to be the result of a recent bad merge.
https://www.geni.com/merge/view?revision_id=79996160760