I'm pretty sure executor no.2 is just a reserve
My understanding is that executors act jointly unless they decide (jointly) that only one will act (the others are still named on probate form and have to sign to rescind the role, from what I remember ).
My DB and I were joint for mum and given he has always been difficult, there was no way I was being sole executor (even though I did all the work) for him to then accuse me of wrongdoing down the line. We were both named for probate and signed for it together (I took a day trip to his nearest office).
We did have my DB and DH sister, but I wanted to remove my DB for a number of years. We held on until eldest was almost 18, then we re-wrote the wills after a massive fall out with DB.
Named SIL still, plus both kids as soon as they reached 18. We may take SIL off in future, but in reality the kids would likely do it together.