How to properly increase system partition on Moto G xt1033?
It is not possible. 

Adopted storage works for marshmallow version and later. You may not use it on jellybean or even if you updated to lollipop.

I might​ have been wrong in understanding your situation, so please let us know of root status and latest rom or android version you have.

There is also more complexity when creating more than two partitions.
Try what has been discussed in https://android.stackexchange.com/a/145458/90095