Hello!
I just returned on Sunday from organising a group of 60 flying over to Italy and back with BA. We weren't able to "block" book any seating as BA wanted to charge for this, so seat allocation was undertaken at check-in in T5 and Bologna on the way back. I was able to seperate some individuals from the group reservation and onto their own locator if they had status or wanted to pay to reserve seats.
I'd advise that if someone wants to sit next to another, that they checking together - and the agent will then allocate their seats together. That's how we got around that issue!
Good luck!