To take what TWest mentioned a little further and maybe help explain things to other not familiar with all this .....
If anyone thinks that all these filters will stop everything, it will not but the odds are much better than a single unit. Installing two filter does mean two of the same purpose, just means two ..... Just added one for water separation, and one for particulate filtering. Add a second filter for particulate, then you have two filters doing the same function, one protecting the other .....
This is why you stage your filtering, this why on large vehicle you see so many. If the first plugs up for what ever reason and goes into bypass mode, then the next catches it and so on ..... Staged filtering does not stop everything but the assurances that the last filter will stop the contamination its designed for while everything else fails is much higher than a single filter will ever achieve. You will never achieve 100%, but you will approach 99% if done right. So single filter is 50% chance, goto to two (of the same purpose), you go to something like 70%, goto to three of the same purpose, you can go to 90%, etc (numbers are not exact but get the idea, wife screaming at me to go so have to rush

).
Using my setup as an example:
I have 3 water separation filters (one serving dual purpose), in a staged level (20 microns down to 10). Two can fail and I still have some level of protection vs one only and not that good to begin with.
I have three particulate filters (one serving dual purpose), in the same staged level (10 microns down to 2). Two can fail and still have a good filtration level better than factory.
Hope that helps explain why so many filters and the reasoning behind it. Can explain more later tonight if it helps. I know others here can also
Cheers all.