Then you merely need to merge the two profiles into one.
https://help.geni.com/hc/en-us/articles/229705547-How-do-I-merge-du...
Read that. From how I read it they both have to be visible to do that. In this case, he was first father of the husband of the lady in the family line so he is visible when you look at the husband's tree. Then he married the aunt of his daughter-in-law which makes him visible in the main tree at that point. But both positions are not visible at the same time.