I tried looking at the document link above but I don’t have access, maybe turn on public access for viewers?
The newly announced Jupyterlite notebook custom widget sounds like it might be helpful for this. You can write Python code to pull in data from multiple tables using await grist.fetch_table(table_id) and then do whatever you want with them, e.g. combine them into one pandas DataFrame and then feed that into the plotting library of your choice.