When the executors apply for probate, they ALL have to be accounted for on the probate application form. It just isn't possible for them not to be, because the Registrar checks this carefully and won't issue a Grant unless they are. The form also contains options for an executor to either have 'reserved powers' or to 'rescind rights' completely. In both of these situations, the Registrar will also want a signed form by those executors confirming that what is written on the probate form. This is the foolproof way of ensuring one executor doesn't run off and get the Grant of Probate without the others knowing. It is pretty unusual that all the executors don't attend in person at the application interview. This is the point at which the Registrar takes the original Will and keeps it - attaching a copy to the GoP.
I can't help you with a Will that doesn't make sense to you - but if your brother is named as an executor the solicitor should surely be helping him to understand it - at a cost, of course.
For simple affairs, if the solicitor was not named as the executor, I don't quite understand how there is a solicitor involved at all. Did your step-mother fix that up?