shein: Which Rabbonim? I believe Sam2 (I’m taking him on faith here) quoted some very reliable sources that do not hold with that.
And as for coercion – this has already been discussed extensively on this thread. What they are doing is illegal. Saying “so don’t take the bus” just doesn’t cut it – they have a RIGHT to ride that bus, and you DON’T have a right to make them do anything.
Again, let me say that I am not against separate seating. However, if you are going to break the law to enforce it, that creates a big chillul Hashem. And there is no clear evidence that suggests that that is warranted.