Are all of the windows in brick veneer? So there is going to be brickwork anyway? I'd agree to change them all to new. Replacement windows leave you with too much frame and smaller glass.

shead, do you have any pics? Its very rare for masonry to extend inward past the RO where it would prevent a larger window from being installed.

As far as aesthetics, you will want things to match, however there is some flexibility there depending on the surrounding siding/masonry. For instance, if these two in question are in brick and the others are surrounded by siding, a different look from the exterior would look more attributable to that to the average person... but again, it would be uncommon to need masonry work just to install a window sized for the RO.

Replace them all, like @HomeSealed Exteriors, LLC stated it is uncommon for replacement to require a masonry work.

This is the house now:

Windows in red will be staying.

This is a crude sketch of what the front will look like once we add onto the back left corner of the house and also add about 8 ft onto the end plus another 6 ft (the indented) area for a mudroom and a carport. The front will be all brick.

I had new Marvin windows installed in my house. The 2nd floor was done about 10 years ago and all used were "replacement" windows. They went on siding.

Two years later, the ones on the first floor were done. The LR windows were enlarged - brick work did not have to be done as they had originally been designed to have a panel below the window; now it was window with just a small panel below. The rest of the windows were replacement on brick except for the double window in my breakfast room - it was a new window. They had to construct a new outside "sill" for it but since the brick is painted, there was no problem matching. Then two years later, I realized I should have done a long 8 over 12 window in the other front-facing room, my library. So I tore out a perfectly good Marvin window and had brick work done so I could put in an 8 over 12 there as well.

I can't really tell from the outside which is replacement and which is "new". Inside, I really am not fond of that ridge Marvin puts on the window sill. If I had it to do over again, I would have had all the windows put in as "new", not replacement. Probably no one on earth but me notices it.

It looks like you have conventional brickmold there Shead. No reason that the window can't be sized to fit the RO ("new construction size"), although you could also mimic the look on the units added to the addition even if you do pockets in those and NC on the others. If your main objective is to simply make things look uniform, I'd simply have a conversation with your contractor about that and come up with a game plan either way

Thanks everyone! I'll definitely check with the contractors and window dealers (I need to decide which brand I want to use for that too but that's another post.)

Shead, same boat here...large addition/remodel, some old windows with brick. We ordered custom size windows for those ones and they look fantastic, like they were always there. Sure, installation was a pain but husband got it done. All the rest of them are new construction and standard size.