Upgrading 4 seats to an 8 seat cabin would be pushing it in most situations.
For sure, I have managed it once out of 4 attempts. I watch the seat map multiple times a day, and can usually work out who got upgraded..
On my recent MEL-NAN flight, I ended up moving 2 of us into 3A and 3B when they got upgraded....
I made a comment to the new people in 2A and 2C and thanked them for giving up their seats, they kinda understood me....
However, the person in 3C was not happy, and they made a comment to their other seatmates in 3D/E/F that I must have paid for the seats in 3A/C and she wasn't happy as she thought they would be empty or others further back could then pay to move into 3A/C
After we got chatting, I told her that I was platinum and picked the seats for free when the others got upgraded. She wasn't that impressed
As it turns out a family/friends group of 8+ of them were bidding for upgrades, I told her I gave up at $350 and she laughed, as the group of them were bidding against each other and it ended up going for $900 each.... I didn't comment on the value of that, when they told me they paid $500 each for the Y tickets..
She hadn't been in row 3 before and after a while she commented that it was better than Row 1 and 2 and I said, exactly why I picked it for free.
Now that FJ fly their A350's into MEL and the J pricing is cheaper than VA on most flights I'm flying to FJ now