Late 90s Macks - 3 filters on driver's side, with air lines?

I'm not a Mack person at all, and now that I have to work on one for some time I am finding out that there are some MAJOR differences between them and well...on the left side of the motor, the driver's side, there is a filter housing with three filters and one sensor with a 2 pin wiring harness. One of the filters has a hose connecting it from the bottom of the filter to the block. Another has a braided line connecting it from the top at the housing up into the firewall and that has the words air brake written on it, but this is not an air dryer. The vehicle has a Bendix AD-9 system on it which I already changed the cartridge on. These filters on this truck are so old, there aren't any numbers or anything, but it seems like there's a leak. Anyone know what they are? What they go to? Anything about them? The best I can find are a few off hand references to "twin filters" on the driver's side of a Mack, but these are triple filters, though they're on the driver's side, I assume the extra filter means something. There are no lines other then those I mentioned, so I really don't get it. It seems they share a single housing, but what needs three filters? What goes from the air brakes to the engine block? Unless that's an incorrect line, which makes a bit more sense to me, but still leaves me with the big question of what are they and why are they there.

 

E7-350 is what the tag says. They are colored like the fuel filters (located on the far passenger side frame rail on this model) and this is not Centrimax style (though I haven't found something of that kind yet, haven't had to PM yet). They're regular spin ons, and they look a heck of a lot like the fuel filters except for the one with the line to the engine. I did find PS, coolant and hydraulic filters already. It's not possible this thing has 3 oil filters?

 

This is my awful picture of them, but it's kind of dark in here. This is left side of motor right in front of firewall. 3 oil filters? I've never heard of or seen such a thing, but I believe it. Mack can be strange sometimes.