Furlough and job title

[WhatAboutThisTwo]

If you have a number of people all with the same job title and pay, is it OK to furlough some but not others (no rotation)- the rationale being that day-day-day they actually perform quite different functions?

If the situation then moved to redundancy, would those that had stayed working be able to use their 'function' as an argument to be kept on, despite on paper being the same as everyone else?

Yes you can furlough some of the positions but not others.
Are the differences in their roles recorded somewhere, such as due to different work times, patches or additional tasks they've taken on?

Entirely up to the employer who to furlough, assuming they meet the criteria for doing so.

The fact someone is or isn't on furlough will be irrelevant when it comes to redundancy decisions. Impossible to say without knowing more, but for roles to be pooled together for redundancy selection purposes, they don't have to be exactly the same.