Yes, you can use 2 4G SIM cards at the same time in Nokia 8.1.
Yes, Nokia 8.1 does have the EIS. It also has OIS also.
Yes, Nokia 8.1 does have the 3.5 mm headphone jack. It also has Bluetooth A2DP support.
In the official packaging of Nokia 8.1 - you will get your Nokia 8.1, USB Type C cable, Power adapter, Headset, Quick start guide & SIM door key.
Yes, Nokia 8.1 display works as a flash under low-light conditions.