hello Ingrid -
We just got back a couple of weeks ago from the states.
For international flights you still need to check in at the departure counter from your airlines.
They only ask for your passports and then you will receive your boarding pass.
On our return flght they didn't even ask for the etickets, just the pasports.
The reason for the etickets is it saves everyone alot of time and paperwork ...
don't know how it work here in Europe but in the states you can check yourself in with etickets for domestic flights, as long as you have the number on the eticket and your passport ... you''ll be ok.
You might want to check with your airlines, if you have anymore questions ... usually on thier site they'll have a place called "contact us".
Good luck and have un in the sun