I mean a 4 foot by 4 foot window on each side!!

Being near a tub, I'd recommend using Andersen's casement windows. To fill a 4x4 opening, use the C24 unit on each side. Something to remember: being around a tub, your local building codes will probably require the glass to be tempered.
The great thing with Andersen's casement is that the sash are clad inside and out, so they are protected from moisture. If you get the prefinished white interior, you can get the inside stops wrapped in vinyl as well, further protecting the units from the high moisture area.
Hope this helps. Good luck with your project.

If you want windows that open, why are you getting windows that don't open? Being able to open a window (especially in a bathroom)is important. I'd never go for that. Sandy

Thanks Mike, That is what I am going to do:0)

Each 4ft x 4ft opening would need two 2 x 4 casement windows or one 4 x 4 awning window. Considering that such large windows provide a great deal of ventilation without being opened very far I would choose the awning windows especially since they often have a neater appearance from outside when open and also eliminate two vertical posts.

That's another viable option. The AP42V fits the 4x4 opening. However, the ventilation area is significantly smaller. Due to reduced travel, the awning only offers 1.8 sq ft of ventilation. The C24, in comparison, offers 10.8 sq ft of ventilation with the sash opening a full 90 degrees.
The C24 is also 2 sash in 1 frame, with a mull post in between that the sash lock into. This design offers a greater design pressure rating as well, coming in at a DP50 compared to the awnings DP35. The awning would only eliminate 1 vertical post.

There are many good choices for this application. I never did understand why most builders put those fixed units around the tub. The are only there to let in light from the outside. It's always nice to let the fresh air in to ventilate the bathroom. Especially after a bath or shower to help exhaust the steam. I personally like the Awning type window in these locations. It vents at the bottom and can be left open without any concerns if it rains. Crank outs and Sliders are also functional here but they both add a vertical post to the viewing area. If your tub is in a nice wooded area to look out over. You want to be able to have a nice glass of wine and watch it snow outside while your relaxing in the Spa!! Good Luck!!!