While browsing through my tree, I rediscovered that two younger half-siblings to my great-great-grandmother (last name: Haase) had spouses who were siblings (last name Baker). I added the relationship to my list of “double relationships” that I keep.
This double-relationship they have with each other probably does not impact my DNA match analysis. Probably.
If a close cousin of the Baker siblings (who are not related to me biologically) married a close cousin of one of my great-grandparents (very reasonable in my ancestral neck of the woods), then descendants of that marriage could be DNA matches to me. They could also be DNA matches for descendants of either of the Haase-Baker marriages. So the descendant of a Baker-cousin to my g-grandparent marriage could be a shared match I have with the Haase-Baker descendant.
Just stuff to keep in mind.