Libgdx -2D Tile game - Scaling images with resolution?

If I am using all my graphics for 1024x768 resolution, how can I make it so that if I change the resolution, my images scale up/down in the correct ratio?
I know how to do it with images who fill out the whole screen with Gdx.getScreenWidth etc.
But how can I scale the smaller images like enemies etc?

Another thing, how do I keep the viewsize of my game the same? I draw my map from 2D int Array. Tiles are 64x64 big.
With 1024x768 resolution I can look like 15 tiles left and right. 8 tiles up and down.

But if I change resolution to 1920x1080 I can watch like 30 tiles around the player. I want thatthe vision radius stays the same as in standart resolution so its fair for everyone.