two ports into one

This would be 2 ports but they are in the middle

You couldn't.  But you could certainly design a dual-driver single ported enclosure using those speakers.

That's what your latest pic is, a dual-driver single ported enclosure. Usually it's best to have each sub in thier own enclosure, like first pic you showed. The reason is because if one driver was to fail, the other wouldn't be affected by all the extra airspace (for both of them).

You would first have to answer this:

How long must the port be while keeping port noise in check?  And, is this length a few inches less than the inside depth of the box?

If yes, you would fit two baffles at the center of the box that extend from top to bottom.  The distance between the baffles is slot opening width, just the same as if you put the port along the side of the box.  You would need a few inches of free space at the end of the port.  The box is a single chamber, not divided.

But if the port must be longer than the box can be deep, you can't do it in the center with one single port.  You would instead use a dual chamber box with dual ports as I am an idiot illustrated, or put the port off to one side.

I don't accept your last illustration as a proper vented enclosure.  It's a muddy mix between a single chamber and dual chamber and I wouldn't count on the port response accuracy.  My opinion is that a multi-driver single chamber enclosure must share airspace other than that which is comprised of port airspace.

How about adding one more piece of wood and have it look like this.