I know I'm jumping in late, but the last time I replaced 2 side by side double hung windows, I build a deck outside the windows and replaced them with a sliding glass door.
When we moved into my current house, there was a pair of double hungs looking out over the back yard. Due to the slope of the lot, the yard is 6' below the floor level of the room.
The only ways to get to the back yard was to either go out the front door and around to the back, or down the basement stairs - which landed at the front of the house - and then make U-turn, go all the way through the basement and out the back door.
I told my wife that the only way I'd buy the house was if the very first project was to build a deck and replace the windows with a door. We moved in in April and broke ground the next weekend.
The family before us had lived in the house for 30 years and rasied 4 kids, all that time dealing with inconvenient access to the back yard. It's been 25 years since I built the deck and we still love it.