If your boyfriend won't tell them to stop, then he's not worth keeping and will just be another child for you to deal with. If he won't stand up for his pregnant girlfriend while she's being threatened, then sorry, he doesn't love you and isn't much of a man.
Refuse to have any contact with any of them, any threats, call the police.
When baby arrives, resist the urge to go show him/her off, keep your child away from such poisonous people, refuse to see them without a suitably convincing apology, and even then, minimal contact for the rest of your life.
There's a good chance once it's clear you are actually pregnant, they will go from saying "she's not pregnant" to "it's not [boyfriends]". Don't engage, to others "they are wrong but I'm not going to try to talk them round."
Ignore and stop letting them be part if your life.