Ok...here's a concept. If you want a good shot at having the seats you want, fly a different airline! If there are more than two of you flying, and you just have to sit together, in a specific area of the plane, book with an airline that allows you to choose your seats. Now, understand, those seats can change! I booked myself on a Delta flight from Boston to Orlando many years ago. About a week after I booked, our family situation changed and I was able to take my dd with me...but that meant booking her on a different reservation. No biggie. Got her seated next to me. No problem. Well, not until a month out from the flight. Delta cancelled the flight we were on, and combined our flight with two other flights...one of which was the original flight I wanted but it was a lot more expensive than the flight I chose. I saw that I was put on that more desirable flight, but dd was put on a later, less desirable flight. Of course, the Delta computer didn't realize we were really traveling together...it saw two different reservations. I called Delta, got us both on that same more desirable flight. BUT...our seats were nowhere close to be where I had wanted to be seated.
So, even if you book a legacy airline, and choose your seats, they can still make equipment changes that can, and do, change your chosen seats..and scatter your group all over the plane.