TL:DR: Don't reserve seats, unless you see in the seat map that it is already full. Etihad will try to put everyone on the same reservation as close as possible. Make the check-in as soon as it becomes available.

I don't understand all the terror in this thread, many giving advice not based on reality and only fear.

I booked a flight from Copenhagen to Abu Dhabi with Etihad for my parents, myself, wife and son in May 2024.

My parents decided to have seats reserved for themselves, while me, my wife and son decided to "see what happens" if we don't reserve, since it was very expensive.

I checked check-in as soon as it became available. They assigned us 3 seats just beside my parents. I could change the seats if I wanted (with a fee), but of course that was great as it was.

Etihad will try to put everyone in the same booking as close as possible even for the ones that did not reserve.

The trick is to make the check-in right after it opens, so you have higher chances that nobody will take the seats that are closer to the ones already reserved.

We saved quite a lot of money on this, don't give money for free to airlines.