You're right. Bad choice. The maroons are the most aggressive clowns, so perhaps should be added last. The pipefish are timid and need low flow generally, and can be hard to feed. I'd take them back, and consider taking the clowns back too - or maybe sump them and add them back in later.
Seems like you've had some poor advice. Remember shops are there to sell. Some really don't care. Others are excellent.