Wow, very cool! We had our first taste of Civil War history on our winter Florida trip, I'd never been to this area of the country and although I read a lot about history, there's something about actually being at these sites that make things feel more immediate and real. I can't imagine how terrifying it would have been to stay in that house during the battle, but I can see why people did it, if they left they would lose everything.
You can resize images online here: http://resizeimage.net/ I've used it a couple of times when I'm on my tablet instead of a computer with Lightroom or Photoshop and it's simple. Or, if you are using any photo manipulation program, they all have options to save smaller versions (just don't save over the original, make a copy with a different name).