Hi Jim
As you perhaps already know, WikiTree has different standards for the quality or reliability of sources. For those profiles born 1700 and after, then even unsourced family trees from FamilySearch, or elsewhere, are acceptable to at least start a profile. However pre-1700 profiles have to have reliable sources.
My personal opinion is that for those profiles born before 1700, even if the FamilySearch tree is sourced, it is still better to actually try to find and cite the original source/s.
Also, it is my understanding that FamilySearch profiles, like WikiTree profiles, can change over time, people can add sources, remove sources, change some details etc, and you might like to consider whether the FamilySearch Family Tree is going to remain, as it is, at the time you cite it on your "in laws" family profiles?