“Quarantine” can 2 homes quarantine together?

My neighbors keep playing together in our community spaces posting tons on social media they don’t have covid so their 2 homes are quarantined together so their kids can be together. Even their friends post “not social distancing I see” and somehow in their reasoning they feel like their garages are a shared space so they can be together.

How do they know they don’t have covid when you can’t be tested unless your severely ill? Also how do they know I don’t have covid? I’m pregnant and go to the doctor during the pandemic. They keep spilling into shared spaces including my porch furniture.

I’ll let you be the judge - can someone explain this “logic” to me?