The very top looks like the water polisher that I don't typically use in a Reef Setup - they claim it is for better water taste.
The second to top one is actually your RO Membrane. No need to change that one as frequent. Just give it a flushing if you can.
If you are getting limited amounts of water out why not just take out the first 3 bottom filters and see if your output resumes just so you know where the problem resides?
Banged my head many times with RO problems, hopefully this helps.
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