Yep, I misread what you are doing. So when you select just those two members on rows with the same measure, they return values but when you use them in the calc member, it doesn't?
Yes, when I use the two members on rows, I get the total of sales for each of those two members.
When I use aggregate, I get no output for that member.
I thought this would have been a common requirement: to simulate new members that are the sum of siblings.