1) Is khums divided exactly in half to Sadat and half for Imam? I mean, 10% Sahme Sadat and 10% Sahme Imam?

2) The above question is true according to all Maraji or is there a difference of opinion among them?

3) Is it needed a permission from the Marja for Sahme Sadat? If I want to give Sahme Sadat to an organization that distributes it among poor Sayyed, does the organization need an Ijaza from the Marja?

4) If I need to pay khums for multiple years, let's say 4 years, is it necessary that I make a different payment for each year or is it ok if I pay it all at the same time (one payment with the intention of khums for the 4 years)?

by

1-Yes it is equally divided in two halves both parts are exactly 10%.

2- it is according to all Maraje.

3-for the distribution of sahme sadaat permission is not required according all Maraje except Aagha e Khamenei
As per the ruling of Aagha e khamenei. You must deposit to his office or his representatives.

4- In this case contact Wakeel (representative) of your Marja