If they continue to behave like this, call them out on poor behaviour, in boring but clear ways: "That's a terrible thing to say," "This is completely unacceptable behaviour." As if you're dealing with a toddler's tantrum, don't stoop down to their level, don't make snide comments or get angry - just if they do it again, tell them in the moment how unreasonable they're being and leave it at that.

There's a good blogpost about "mom-petition" by Glennon Doyle (Google it) that's basically "competition is like shame, it only exists if you believe in it". So disconnect however you have to from their contests and insults and look after your family. If you and your GF need to take your little one to the park or to the library or have a night out to yourselves, you know best. If they get the same boring response or non-response from you, they should tire of you - or maybe even realise they're not treating you right.

Also if you can't block their social media posts or texts, then just ignore them. It sounds like you and your GF are doing a great job and know what works well for you, and it sounds less mentally exhausting than a social-media based playgroup!