If I understand right you want only the icons, right?
Use Winrar (it's the one I use) and just open the apk with Winrar. Then go to /res/drawable-xhdpi (or drawable-hdpi, it depends) and search for an icon called "ic_launcher.png", it's the icon of the app...
All the apps, as far as I know, have this icon named like that for their icon as you see in your app drawer for example, maybe just the location could change.
Then you can use the icon to replace another one.
No need to decompile, just open the apk with Winrar, or at least with Root Explorer you can also (but for me it's more convenient on PC), click on the apk, then display and follow the same path, when you find your icon-> long press then extract.