Question: I want to know how to install two bluestacks in a system and then run it.

Is it possible to run bluestacks in Virtualbox

Answer: 
Bluestacks is an android emulator. As with any emulator it is very heavy on system resources. In addition, bluestacks installs services that remain active constantly.

For that reason, no, you cannot install 2 bluestacks next to eachother on a system. You might be able to run bluestacks from a different user and be able to have a different profile.

Also, you should not install bluestacks in a virtualbox because that will make it way too slow to be using.
You can run directly android on VirtualBox I have tested and it's working very well. the version 4.4 r2 is a good one
You can find some iso [here](http://www.android-x86.org/)