1) You are correct that the force does not depend on the absolute position of the twoloop system. Listing x is just a formalityhe specifies that one small loop is at x and the other is at x'. The important part is that the equation contains only the difference xx', with no dependence on x itself.
2) I'm not following your question. Eq. (1.15) is not about force, it just shows that div B =0. This really doesn't depend on the current, following instead from the vector calculus relation that div(curl v)=0 for any vector v
