Thanks for speedy reply, in that case can I operate with dual install on same Hard drive, install of FSX and Prepar3d, with FSDT in each, would that require dual license of FSDT or are licenses good per user or per sim install...
No FSDT product license has any relationship with the sim (or the sims) they are installed into.
The activation is tied to your *system* so, you could have FS9, FSX, FSX:SE, P3D 1.x and P3D 2.x all installed at the same time, each one with a separate installation of FSDT sceneries, but you will still use 1 ACTIVATION per product. If you dual-boot two different copies of Windows, instead, you will need 2 Activations.
Note that, installing two copies of the sceneries under FSX and P3D won't change the requirement of having to turn off the Legacy mode of the Migration tool, it will still be off when you run the scenery, it's not an installation issue only, the correct sim must be detected when it starts.
What is best way to have sceneries installed in both on same HD, just run installers in each or is there a way to share some files in order to save disk space....
Just run their installer, and turn OFF the P3D Migration Tool when you install, so the installer can detect P3D properly and giving you the option to install there.
Some of the latest sceneries like JFK V2, KIAH and CYVR already install some files in a shared location, but you cannot otherwise move files manually after the installation, because they must stay in the fsdreamteam folder, under the folder the sim is installed into.