36x80 prehung, what size rough opening?

I just had vinyl replacement windows installed.The 10 double hungs look fine.I also had 2 sliders installed.The front slider is quite large and is a 1/4 1/2 1/4 variety.It replaced a picture window with a double hung on either side.The rear slider is smaller and replaced 2 double hungs next to each other that had wood between them.The problem is that the new sliders are bowing in and don't look square,after I pointed this out the installer zipped a screw into the middle on the side and it improved it but it still doesn't look right.Not too mention that it screwed up the way it looked on the inside.they are trying to tell me its ok ,but it doesn't seem right to me.Also, my wife says that they looked bowed even before the install!!!!I did not pay them and want this fixed,what should I do and what are my options....thanks..

We are replacing a solid pane 48 x 48 double pane unit in our bathroom with a glass block unit which is 40 x 40. We have brick veneer on the outside. Unfortunately, the window company I have purchased the replacement window from does not do the opening reduction job. What do I need to do to reduce the opening to the 40.5 x 40.5 the window company says I need to have for them to work with? Do I need to remove the sheetrock from around the window opening or can I just frame on top of that to make the opening smaller? Also, do I need to just make the new opening flush with the existing aluminum window frame with respect to how far (remember, it is 48 x 48 and I will be reducing the opening almost 4 inches all the way around) it sticks out? Will I need to remove the existing aluminum frame or can we just trim over it after the new window unit is installed? The glass should come right out as the outside window frame has screws that retain the outer frame to the inner frame.