Survey of online trees

I am doing an indirect evidence case study to prove parentage. I want to mention that a survey of online trees was done but no tree was found with a source for the parental link between the two generations. I would like to simply cite the Ancestry Public Member Trees, FamilySearch Family Tree, and My Heritage Family Trees as a whole and not list every single tree that was examined. Is that a legit way to handle it? I think listing 40ish trees in a citation would be overkill but I thought I better check :) 

"Ancestry Public Member Trees," Ancestry.com (https://www.ancestry.com : accessed 22 February 2019); "Family Tree," FamilySearch (https://www.familysearch.org : accessed 22 February 2019); "Family Trees," MyHeritage (https://www.myheritage.com : accessed 22 February 2019).