Nothing in life is perfect. Everything is a compromise and what works (worked) for me may not represent your ideal solution. Having said that, here we go ...
OK, first for what I use:
I have a Sony A6000 in a Nauticam housing. For wide angle, I have the
10-18mm lens and the 7inch dome port. For dives where I expect a little of everything, I use the 16-50 kit lens and for macro, I just received (but have not yet dove with) the Inon macro wet lens.
Next how did I get to that decision?
I tend to shoot primarily wide angle under water. Even when I shoot macro, it is more often than not more of a "Close Focus Wide Angle" (CFWA), rather than a true macro image. Because of this, I wanted to build my set-up focusing (pardon the pun) on wide angle. I was able to eliminate the Sony 16mm f2.8 pancake lens (with or without the WA or FE adapters) pretty quickly after just about every review I read talked about it being soft. The 20mm pancake appeared to be a little better but not much. I saw little to no benefit to using the Sigma 19mm other than it had an aperture of f2.8, and I would never shoot wide angle at f2.8 because of the narrow depth of field. I also eliminated any manual focus lens since I knew that for me, I would hate the constraints that such a lens would impose under water where I could not focus and would have to rely on an image being "close enough to in focus". (This is not a limiting factor above the surface in any way, and Samyang/Rokinon are known for making some very respected lenses used in astrophotograpy including the two you mentioned.)
This left me with basically two choices: the 16-50 kit lens and the 10-18 lens (the Sony/Zeiss 16-70 was also briefly considered and although it was an amazing lens, and maybe what I should have opted for, I ruled it out). So, for most dives, I hit the water with the Sony 10-18 and a 7inch dome. It does not give any vignetting and I can shoot it all the way down to 10mm (the equivalent of 15mm on a Full Frame sensor). I do not have a zoom ring on the 10-18mm, I set it before I load my camera into the housing & then shoot it as if it was a "prime lens" from that point on. On dives where I expect to run into a variety of subjects (Split Coral Head in the Bahamas comes to mind with everything from Christmas tree worms to a healthy Reef Shark population) I will put on my 16-50 kit lens (and zoom ring) and live with the fact that I can not get wider than 16mm, but I have much more on the "long end".
So, What would I recommend for you?
The first thing I would recommend, is that you read
this review. It is not for your camera, nor for your housing, but I think that it might have a lot of the information that you are seeking. It discusses shooting the Sony 16-50 kit lens underwater with wide angle wet lenses. (See that? My first recommendation didn't cost you a penny!)
Next, I would likely opt for the 16-50mm kit lens either with a wide-angle wet lens or on its own. It is reasonably fast and relatively fast focusing and will give you a lot of versatility (including OSS) and with very few limitations.
Here are a couple pics I have shot with my 16-50mm lens (on my A6000):
First, although you are looking for wide angle, here is a macro shot of a Christmas Tree Worm simply to give you an idea of the range you can expect in practical terms.
On the same dive, I also shot this Caribbean Reef Shark:
The Christmas Tree Worm was shot at 50mm and the Reef Shark was shot at 16mm. Neither had a wet lens on the port.
Ultimately, only you will know what is right for you, but if I were to make a recommendation, then it would be the Sony 16-50mm kit lens with or without a Wide Angle Wet Lens.
Good luck in your search.