I just had pretty much the same scenario. I had chosen my coveted 2C. I thought it strange that this couple kept storming the boarding gate despite being sent back twice when they had called only for preboards, families and active duty military. The third time, the GA just let them board. It made sense when I boarded and found the woman ensconced in my seat, blanket unwrapped and over her knees. She said she wanted to sit with her husband and I could take the bulkhead. Um, no thank you. I said I was happy with my seat and she made a bit of a scene. They were last minute upgrades, by the way. I just moved to the front to let people behind me pass and told the FA. The woman tried again to stay put, saying all seats are the same. In the end, she huffily moved and they managed to convince two other people to move around and ended up in 2D/F. It frosts me when people bully others into getting their way.