Okay, so in Fyre we are introduced to the characters of Edmund and Ernold Heap, a pair of identical twins who are Silas' brothers. The most important thing about them, from a plot perspective, is that they are identical twins; because they are twins the Ring Wizards are able to Consume them, because they are identical it takes them longer to be Consumed.
This gets me to thinking, what if, instead of introducing two new characters at the last minute, Angie Sage had placed the identical Heap twins we are familiar with, Ed and Eric, in the same situation. It would have been a heck of a lot darker, having characters we've known for seven books forced to fight their family and play the the villains, and probably a lot more traumatic for Simon, Sep, and Jenna, confronting the brothers they've known for years rather than the Uncles they've just met.
I also wonder if this might have been Angie Sage's original intention, she seems to go out of her way to get the Forest Heaps back into the Castle, and even has Silas suggest they train as Wizards. Everything is set up for Ed and Eric to be at the Wizard Tower, on Seal Watch, ready to be consumed, but instead these unknown Heap Uncles appear at the last minute. Not to mention the fact that Ed and Eric, and Edmund and Ernold have similar names, both starting with 'Ed' and 'Er' respectively, the sort of similar names that might easily have been changed quickly using the 'Replace' tool on a Word document. Maybe she wanted it to be Ed and Eric, but the publishers asked her to tone it down, to avoid traumatising her mostly child audience.