How many funerals have people seen on TV where the deceased is extremely well known and very well liked and the route of the funeral cortege is lined with hundreds of people paying their respects? I really can't see that the presence of a military band is really much different in virus spreading terms.
Outdoor gatherings of lots of people, such as the rush to the coast last summer, have NOT been associated with any superspreading of the virus. The bandsmen will be fine, especially if there's a bit of a breeze to blow the aerosols away.
As for the 'It's not fair', brigade, well, it's not fair that 53% of voters didn't vote tory in 2019, or that 48% of voters have been yanked out of the EU against their will. As we are incessantly told, 'Life's not fair'; so let's hope they get over it in much the same way that we in the 53% & 48% have had to...