Ok first off, all versions of IL-2 will allow you to play co-operative mssions or dogfights. But everyone has to have same version as the guy hosting.
The co-op missions allows you to set up a fly a specific mission. And with co-ops you can have multiple people in the same plane. But once you get shot down, you can not respawn.
Alternatively you can create a dogfight mission and set home base for just one side and make all enemy flights AI. With this you can not share a plane with someone else. But if you get shot down you can respawn.
I recommend looking for missions at:
www.mission4today.com this sight has plenty of missions and other goodies.