Thanks for asking, @lpb!
Hi @EmmanuelY, I’ve had a look to the comments and I think the steps you shared in your last comment are the right ones and the more straightforward for what you are trying to achieve.
One thing I want to note is that if the Members you will remove from the Organization and re-invite them as Guests have any tasks assigned, I recommend you creating one project for each user to save their previous tasks so you can easily assign the task back to the Guest account by adding them to the project. This is just a tip to make sure they don’t lose information.
I also encourage you to contact our support team if you have any questions or issue through the process: How to contact our Support Team ✉.
I hope this helps! 