Shawn,
I will ask the theatre to make a joint.
But I have another important question.

Their will be 2 marionette sticks: one for the head and one for the body. But how will be the string-system if there is a joint on the body?

I haven't any experience to make a puppet, so maybe these questions are stupid I only try to think like a puppet-creator

On my dog puppet there was a main stick that had two cross sticks on it. These two cross sticks where strung to the legs so if you rocked the main stick it would move the cross sticks and make the dog walk. The front cross stick could come off the main stick so I could manipulate separate if I wanted. Dropping down from the main stick on cord where two more cross sticks one attached to the back hind and one to the font shoulders. Since these where attached by cord they did not move when the main stick was rocked. I could grab hold of the back drop down stick and move it so the back hind would wiggle like a dog does it whole hind end when it gets excited. My dog had a short tail so no string was attached to it to make it move. Right behind the front leg stick on the main control, there was a cross stick that was attached permanently this was strung to the head. Rocking or tilting the main control made the head move.  It is a bit hard to explain in words but hopefully you get the idea. Wish I had a picture to share with you but I don't. The marionette now lives with the puppet company I used to work with. In fact all my marionettes except one is with them now. Figured it was better that they where used to entertain people instead of just sitting in a closet.

Shawn,

I try to understand your great puppeteer-experienced-explanation, but it's difficult.
A picture or drawing should be helpful for me. Maybe you can try?

I want the best for my puppet
It has to become my buddy!

PS: didn't know, you also play marionettes?