Hello FXtalant,
yes, if you place EAs for Demo trading on 2 accounts they will work on the two. The first ones will not be disabled because you place the same EAs on another account. Actually it is not just for the Demo trading, it is for live as well.
Simply said, the EAs can trade on many platforms, no matter is it demo trading, live trading, or it could be the case you use EAs on demo trading and live account at the same time.
Hope that makes it clearer.