a)
Firefighter (Ff)- Yellow helemt no markings
Crew Manager (CM)- Yellow helmet 2x 12.5 mm black bands with 12.5mm separation 2 x 12.5mm silver bars
Watch Manager (WM) - White helmet 1 x 12.5mm black band and black comb 2 x Large impellers
Station Manager (SM) - White helmet 1 x 19mm black band and black comb 3 x Large impellers
Group Manager (GM) - White helmet 1 x 19mm with 12.5mm black band, 12.5mm separation and black comb 1 x Large impeller in laurel wreath
Area Manager (AM) - White helemt 2 x 19mm black band with 12.5mm separation and black comb 1 x Large impeller with 3mm silver band
Brigade Manager (BM) - White helemt 1 x 38mm black band and black comb role insignia as per original (usually the CFO one)
b) As roles were introduced (from late 1990s they appeared in the Training Strategy Group reports and implementation plans) they REPLACED ranks. So you could not have one with the other. The roles are now in and they do help to remove some of the differentials that occured due to the (apparently anyway) wealth of services. Some had SubOs in charge of multi-pump watches, while others had StnOs - so different pay for the same role. These are now both WM. Your example would only work in some FRS as the rank of the job (the Divisional Commander is not a role it is a job title only) depended on the FRS as did the job tilte. For example we had no Divisional Commanders, we had Head of......., Area Commanders and so on. The roles have given a national description.
c) The different job 'size' is part of the rank-to-role work and there are A and B differentials at all levels from WM to AM. The example you gave is specifically mentioned in the r2r documents. The single pump being WM (A) and SM (A) and the two likely to be WM (B) and SM (B). None of these roles are ranks, whilst they may be the position of certain prior ranks on pay assimilation to role (ONLY for pay purposes) they cannot be related to previous ranks as they are ROLES! The role is the same whether A or B paid and so the role insignia is the same and no difference is taken between, nor is there any development from one to the other.
Role insignia is (supposed) to be only worn on PPE - that is Fire Kit, though most FRS still use it as they did rank markings, indeed many FRS still applyt he old rank markings and all have not yet taken on the role insignia.
c)