Is this normal practice for UA to discontinue a market and rebook you onto a new route entirely -AND- oversell the cabin on that new route? I'd think they would re-book as many in your party as possible J to J, and then when J is full, they'd start re-booking the rest of you into Y. As someone stated, this is NOT an equipment downgrade of the same flight number. The RES agent said all ten of them were confirmed in the Polaris cabin on ORD-KEF so it seems like just a seat assignment issue that should meter itself out.

(I work for DL and we have some kind of RES "offload team" that handles things like this, in advance, to get people to come off of overbooked flights due to schedule changes. Hence I feel its strange that UA would move all of the OP's party, across multiple PNRs, onto a new flight, intentionally overbooking that new flight in J, and then having to later deal with their own offload situation).