I am trying to get 4 business class award seats for the whole family from Madrid to South America with Iberia but it drives me nuts as they only release 2 J award seats per flight. Long story short, I've snatched the 2 J tickets for that flight, hoping that 2 more J seats will pop up closer to departure day but this never happened. There are 2 PE tickets that I can book now via Avios and then try to upgrade them using cash but no-one is able to give me a price for that upgrade. Does anyone have a recent experience or how much it will cost? Obviously we cannot turn up at the airport and have the negotiations at the check-in gate (difference between travelling solo vs with kids ) as -in worst case scenario- we'll end up sitting in different classes!

Thanks in advance