Vasily Andrejevich Engelhardt - Anna Zhukova, Petr Vasilievich, Pavel Vasilievich

I have just noticed that the dates of birth for these people are way too early to be children of Vasili Andreevich Engelhardt. Anna Zhukova - 1740; 1748, pavel Vasilievich 1748. The date of birth of Vasili Andreevich Engelhard himself is 1735. How can it be??? or is it that these children are the foster children but not of Vasili but his two wives? Potemkina ten ears his older - 1725...