Why can't I Resize/Move in GParted?
Solution 1:
To be able to resize/move partitions, the partitions must not be in use.
Boot from a liveCD or liveUSB, make sure no partition is mounted then launch Gparted and create the necessary partition.
After installing Windows you'll have to recreate Grub. The easiest way is to boot again from the live USB, install boot-repair with sudo add-apt-repository ppa:yannubuntu/boot-repair && sudo apt-get update followed by sudo apt-get install -y boot-repair && boot-repair and do a recommended repair.