It is a fair question.
Some airlines, Like Norwegian (www.norwegian.com - who also do cheap flights from the UK to pretty much everywhere) will automatically put together people who are booked to fly together. Yet, if you want to book specific seats other than the seats you have been allocated, you have to pay to book these.
For example, I usually fly with my two kids. Sometimes dh is able to join us, but he books last minute. If we want to sit together all 4, he needs to pay to book a seat near where we have been allocated. We can see this from the seat allocations when we check in online.
I dont know how it usually is on easyjet, but we booked some last minute tickets to fly to Spain with them for half term. Upon checking in, I realized we were not allocated seats together, so I had to pay to put us together, two and two, there were no 3 or 4 near eachother.
I would NOT have come into the cabin and try move heaven and earth so that other people who had booked and probably paid for their seats together should have to move.
Check your seat allocations when you check in online, and if you are not together, book seats. It is not fair on other passengers. It is always a stressed mum who come in to the cabin and start creating a fuss, moaning to the cabin personnel. You really dont want to be that mum!