Peter Jackson was able to film The Lord of the Rings at the same time because he was producing an adaption of a book, so he already had the source material in place. Let's also not forget that he was in pre-production on the trilogy for a good five years before cameras even rolled, years which included a studio change, and a switch from three films, to two, then back to three.
You simply cannot apply LotR to the production of original films that aren't written as serialized installments of one story.