When i open my inventory, and pick up an item, it goes to wherever my mouse cursor is, since im using nucleuscoop to play split screen i cant use my mouse. This makes using the inventory extremely tedious.

You don't need extra tools to play splitscreen. Controllable already provides this functionality. Make sure "Pause on Unfocus"
is turned off by pressing F3 + P and make sure you use virtual mouse for both instances. This will solve your issue.