Is there a way to combine the device memory and the SD card memory together to make one? My galaxy tab pro is no good with 16 GB of memory. It is absolutely useless.
Welcome to Android Central! Sorry, I don't think that's possible. This is why I usually recommend getting devices with as much Internal Storage as you can afford.
There's an app called Root External 2 Internal SD that swaps the memory spaces (so you can use the SD card as "internal" memory ([I've never tried it, since I have the same amount of each, so it wouldn't do anything for me]), but I've never heard of an app, or even a ROM, that combined them. SunOS used to be able to combine hardware into a single "storage", but *nix considers each device (internal storage, SD card) as a separate storage device.