I managed to get the in-laws what I thought was a good deal on flights out to Spain in J through bookwithmatrix with the purchase going through Priceline. It's ticketed by Iberia but 2 out of 3 flights each way are on BA metal. I'm now looking to book them seats (they don't have status) which I'd read should be free on Iberia J tickets but the Iberia site is saying "this flight does not permit seat selection" for all of the flights. If you look at the booking on BA it's offering to sell seats. Is it the case that the BA metal trumps the Iberia ticket or will a call to Iberia let us book seats for all the flights?

One other conundrum is when viewing through BA MMB there are seats assigned on the Iberia metal flights but on the outbound flight for one of the PAX it says "Seat choices are only available at checkin".

Any advice? The route is ABZ-LHR-MAD-AGP which seemed like a good idea at the time as it avoided the schlep from LHR-LGW and rechecking of bags.