u/Suspicious-Angle8152

So I posted earlier asking about having Brood Brothers Auxiliary units and Final Day units in my overall Genestealer Cults Crusade Force, but the question I have now is whether or not I can use the same Tyranid units with all their upgrades from the Genestealer Cults Crusade or if they are supposed to be separate units and loose the upgrades and experience if I field them in a Tyranid Crusade? Or since both the Tyranids and Genestealers are part of the Tyranid/Great Devourer faction that I can add Tyranids to my Genestealer Cults Crusade Force when I get enough points to increase my limit to have two separate armies in my Crusade Force?

So I am trying to build a Genestealer Cult Crusade force and I have a few questions regarding the Brood Brothers detachment and Final Day detachment. When building the Crusade List, am I allowed to have both types of units and deploy them separately like one battle uses Brood Brothers and another battle uses Tyranids, but have both types in my main Crusade army list?