The first thing to say is that this isn’t easy and I’m not actually totally sure what your birds are. There are some obvious pro-Mealy features such as extensive greyish-white in the rump and (on some) a greyish face/neck ‘shawl’. Furthermore, I can’t see any birds showing the giveaway Lesser Redpoll undertail coverts pattern of many short fine streaks overlain by a rich buff wash.
Thanks again to everyone who commented on these birds, thanks to Andy for allowing me to publish the above e-mail, and particular thanks to Chris Townend, who endured all kinds of dreadful weather to photograph and sound-record these birds. I hope it didn't feel like a fruitless exercise Chris!