It sounds like to me they just don't like the new, bigger school and perhaps feel like "fish out of water" there. Is there anyway to put them back at the old school?
They should not repeat preschool just because they choose not to speak to the teacher and students in the new school. In fact, unless a child has serious disabilities, they should NEVER have to repeat preschool. It is "PRE" school meaning before school. The most important thing for them to get out of going is simply how to be in school. Your boys already know that from having been in preschool. So no way in he!! would I have them repeat.
Teachers are always looking for an excuse NOT to work with a child to get them to succeed. If the child is not "cookie cutter" the teacher wants them to repeat which means he/she will just not worry about their progress for the rest of the year because they are going to repeat anyway or they want to diagnose them with something so the parents will medicate them.
Let them earn their money! Unless the teacher lived her life in a bubble, she KNEW or SHOULD HAVE KNOWN that people come in all shapes, sizes, colors and with their own minds, likes, dislikes, etc. If she didn't want to deal with that, she should have chosen another profession. And that is exactly what I would tell her.