It seems to me that you need proc SQL:
create table Merged as
select a.*, b.*
from Member as a left join Sorted as b
The only thing I'd like to note. Instead of my b.* it is better to list all necessary fields from Sorted (e.g. if Sorted contains fields MRGVAR1, A, B, etc. then it should be b.A, b.B etc. MRGVAR1 it is not necessary to list).