I need some opinions on a home renovation issue I have.

We are renovating our kitchen and this involved removing a wall. When
I took down the wall I found not just 1 but 2 cold air returns running
from the second floor above to the basement below. My original idea
was to build a single column to contain the cold air return. Now that
I have discovered that there are actually 2, not 1 I am wondering if it
is OK to combine them into a single column. My idea is to build a
bulkhead to join them at the ceiling and then either have both of them
run into the same place on the floor, or to build a second bulkhead at
the floor to allow each to return to it's original location.

Any thoughts on the best approach?