It shouldn't be a problem on standard service buses. There should be no standees if you're operating to 50%-60% of capacity.

What's not clear from facebook is whether those commenting are referring to the S suffixed services. Unfortunately the Department of Education have disgracefully excluded these services from social distancing, suggesting that all kids are part of the same 'bubble'. But that only applies to dedicated services, which I guess is why GNE have chosen to suffix their schools duplicates with an S.