How could Brandenburg-Prussia get both of Masovia and Silesia, would Prussia still unite Germany if they have both Silesia and Masovia or they would likely get the Polish crown?
The POD is before the reformation Prussia gains Masovia by inheriting it from the Masovian Piasts then Prussia gains Silesia afterwards in a war against Bohemia.When should it happen? Because IOTL after the third partition of Poland Prussia DID rule Silesia and northern Masovia.
You cannot have secular, hereditary Prussia without reformation and dissolution of Teutonic Order. And TO cannot inherit Masovia because it has no rights to it. Either TO conquers Masovia or - like in OTL - after extiction of line of local princes the province returns to Crown.
I'd like to point to the fact that Prussia had nothing in common with Brandenburg until Albert Hohenzollern became first duke of Prussia (since 1525) after dissolution of the Teutonic Order; even after that Prussia and Brandenburg were ruled by different branches of the Hohenzollern family; Prussia was united under one ruler only after the last of Hohenzollern-Ansbach (Albert Frederick) died in 1611; the first ruler of Prussia and Brandenburg was John Sigismund. So first you need to create Prussia-Brandenburg which, as Mefisto noticed, was possible only after dissolution of the Order.