Cost efficient way to add windows to a brick house

I won’t say I'm an expert; I've worked with someone doing something similar in the past and may at least give you some guidance.

Personally, I would use a concrete saw (larger blade than an angle grinder) and/or a chisel to cut the opening. Make sure you have help as you DO NOT want to drop the removed section(s). You can use these bricks later (see below).

Don't forget the header. I know I'm using the wrong term, but I'm referring to the steel plate that holds up the brick over the window.

I would then use a chisel to remove the halved bricks and either turn them around or replace them with good ones from the removed section.

I would also recommend that you at least talk with a mason. They may be able to replicate the detail work around the window with the bricks from the removed section.

These windows must have been installed into window casements that were built in place or reused from previous windows. The reason I comment about that is that if the windows were new units with the windows themselves pre-hung in the casements it is hard to believe that they would have the misfit that you describe as delivered from the factory.

In any case you would do well to see if you can talk one or two other contractors to come out to look at the installation to see what feedback they would give to you.

Sounds to me like you need to argue the case for a replacement set of new windows. If by chance you have not paid for the job you should withhold such payment until the problem is corrected to your satisfaction. If you have already paid then you have lost a certain amount of leverage but threat of a civil suit may be in order if you do not get a suitable response from the contractor. Of course you have to weigh the cost of getting involved in litigation against the size of investment already made in the windows.