I can’t remember if Kindle Fire counts as “PC/Mobile” or if it’s on its own platform. I’ll assume it is and get back to what would be different.
If it’s on the same platform, you can do this with a minor inconvenience. GoW only allows one device to be logged in at a time. So when you put down the Galaxy and pick up the Fire, if you try to play the game will stop you and ask you to restart. Same if you put down the fire and pick up the Galaxy. You most definitely cannot play both at the same time, or if you find a way to do so it’s an exploit.
If it’s not on the same platform, you’ll technically have a different account on each device, so nothing stops you, but you can’t make Galaxy progress from the Fire or vice versa. But I don’t think this is the case.