Tedgrrrr

First time flying Emirates and thoroughly confused. We are flying in Economy and have read that we are allowed ONE piece of carry-on luggage which must weight 7KG or less. Whenever my wife and I travel, we each bring a roll-a-board, and a backpack that fits on the seat in front of us.

Is this not allowed on Emirates? Is it either a roll-a-board or a small-ish backpack? Similarly is it either a roll-a-board or purse, but not both?

Also, how much do they enforce the 7KG leaving JFK, and leaving DBX? My roll-a-board is probably quite heavy, but all my backpack has is a tiny laptop, some charging cables, a water bottle, an iPad, and a camera

Thanks