Depends on how much of the money Disney put in vs. the others. It's like the owners of a company... who has greater control, the two or three people who have 49% control of the company, or the single person with 51%?
It's precisely that reason why business owners are extremely hesitant to have less than 51% ownership of a company.
Disney helping to pay for the production of Doctor Who going forward doesn't give them any degree of ownership of the IP.