Questions regarding Oscar nominations?

These questions are addressed to those who are more knowledgeable regarding the Oscars. So without further ado:

1. 
   

   Can an actor/actress be nominated for both leading role and supporting role at the same time? For example they have a double role in the same movie or leading role in a movie and a supporting role in another movie.

   
   


2. 
   

   Taking the second premise. Can an actor be nominated for leading role for multiple movies( could an actor be nominated for five different roles-maximum amount-at the same time)? And taking things to the extreme(ly fun) can an actor be nominated for all ten roles both leading and supporting at the same time (assuming obviously that he has played in enough movies released in the same year)?

   
   

I know that these are highly hypothetical situations but I want to know if they are at all possible. Shower thoughts I guess. Obligatory: English is not my native language and thank you very much!!!