If you split the booking you will get the Avios back at least, but your friends would lose row 1 in the process, and they won't be able to pay for that row either, it's for Golds. I can't see the point in paying for CE seating, the risk of being split up is theoretically there but I can't remember a recent flight where this happened. And it's a very short flight. What you could do is cancel at about T-36 hrs, at which point even if they were booted out of row 1 (which I don't think is for sure at that point, it would be good if someone reported back on that particular aspect) then there is a good chance of it being available at OLCI stage.

£90 / £180 worth of Avios could buy a lot of compensatory drinks. However there is no implication for doing nothing, if you didn't check-in at OLCI the friends could still do so at that point, and secure their allocated seats, your seat would go to AN Other due to you no-showing.