Generally speaking, Stardock is "OK" with multiple installations for a LAN, as long as you uninstall them afterwards if it's on computers that aren't yours, like a LAN party at a net cafe or something. You are generally permitted a second installation on a computer you do own, in the EULA. It is unlikely, I think, for Elemental to be different. Certainly if it's only between you and your husband in the same house you'll be able to install it on both and play LAN - however, online will require unique serial numbers, so you would need two copies for that.
