Different crimes are proved through different ways. You can't draw analogy between a murder and a white collae crime because both are different in their nature and in the way in which they both are committed. The point which u have completely failed to understand here is that
(i) Hasan Nawaz was dependent upon nawaz sharif
(ii) He had no source of income
(iii) since there was no source of income it was impossible for him to buy such expensive property
(iv) Hasan had to prove that he got that property from xyz source and he is not a mere Benamidar of nawas sharif
(v) he failed to prove any independent source which drew an adverse inference and presumption against nawaz Sharif that he is the actual owner of the property and his children are mere benamidars.
(vi) nawaz also failed to prove that how these properties doesn't exceed his income and means.