DN: Are multiple recruitments possible in the case of Joint Doctorates (DN-JD) and Standard Doctoral Networks (DN) projects as far as the researchers are recruited for a minimum of 3 months?

Yes, it is possible, as long as it is well described in the proposal. It will be assessed accordingly by the evaluators. However, this set-up should not be used to circumvent some other rules, like the 40% rule.