ISNULL, How to display 0 instead of NULL when executing the stored procedure?

My lines are:

select 
isnull(tblaaa.Week,
isnull(tblbbb.Week,
isnull(tblccc.Week,
isnull(tblddd.Week,
ISNULL(tbleee.Week,
tblfff.Week
 )))))AS 'Week'  
,tblaaa.aaa
,tblbbb.bbb
,tblccc.ccc
from

where do i input the '0's?

Tried a few ways but nothing worked.

Any help is appreciated.