I have applied for, and been granted, probate of my late mother's estate jointly with my sister, who is a co-executor.
One thing that I haven't been able to establish, though, is whether the probabe is joint and several, i.e. do we have to both sign everything, or can either of us act alone?
Strictly speaking it's joint and several - but for most purposes (eg routine letters) you will probably be able to get away alone signing 'for the executors'
Certainly when I did my parents' estates the only part my brother played was attending the probate interview and co signing the final cheques.
Maybe it would help if you each had a signed letter from the other saying both of you have the authority to act alone. I'm not sure of its legal status though.
I was executor for my late aunts will along with her son who asked me if I would object to him signing everything even though he lived in another part of the country. No problem at all as long as you sign officially.