I have made an ayahuasca brew from caapi and chacruna and I have been freezing and thawing the brew to get the sediment to fall to the bottom.
That has worked out pretty well. The brews are in separate containers.

Can I decant away from the sediment and still assume that all the DMT is present in the clearer brew? Or can some of it be hiding in the sediment?

Are you going to filter the sediment as well? Otherwise some will be left in the liquid that stays with the sediment and the easiest way to get the most out of the dmt would be to add some more liquid and decant it again.

I had been previously boiling my harmala containing plants along with my light containing plants but found this didn't work well after decanting. The harmalas tend to stick to their sediment so if you decant from a combined brew it won't work IME. Especially if you're using Caapi you're gonna want that sediment, it's the most potent part. The DMT seems to be fairly water soluble though so you can boil 'em separately and decant the Acacia/Mimosa brew.