Please have a look at my dual ubuntu installations. The top one in the photo below is Ubuntu 16.04 and the other is Ubuntu 16.10.
I want to increase the size of root partition /dev/sda2 (of size 7.03 GB) of Ubuntu 16.04. There is unallocated space of 13.41 GB in the bottom part of the partitions as shown in the image. I've to provide space from here to the root partition /dev/sda2. But for that if I create a parition here in the unallocated space and move it to the root partition, then the other installation of Ubuntu (i.e. Ubuntu 16.10) won't boot.
Is there any way to achieve this without having the issue of booting and/or without affecting the boot partition ?