I need advice...

Idk how seriously y’all take covid. It seems some people think it’s no big deal, and the other take extreme precautions. My Dad had a heart attack and almost died a few years ago, made it through only to find out he had stage 4 NH lymphoma...which he also beat after finishing chemo a year ago...then contracted whooping cough which passed but not without leaving permanent damage to his lungs. He is my rock and means the world to me...my biggest reason for taking as much precautions as I can pertaining to social distancing. On top of that, my fiancé is high risk due to health issues along with my 9 year old daughter...our 11 month old son obviously has no immunity and I’m pregnant as well which puts me more at risk. We social distance and wear masks...and we don’t surround ourselves with people. My children are homeschooled...by whatever means necessary we try our hardest to avoid any contact with covid. Here’s the pickle...my fiancé has two other children with his ex...who takes NO precautions and believes it to be a hoax, conspiracy theory, whatever...she gives no fucks...constantly has friends over, goes to bars and restaurants and allows their children to stay with friends and vice versa. It’s caused hell...so much so that he didn’t see them on his weekend but for a couple times in the last few months because we didn’t want to risk it. His daughter has been really upset about it and doesn’t understand, basically feels like he doesn’t want to see her and compares people she knows who are high risk and still see their kids to him to make him feel bad. I understand her pain but this shit scares me. A couple weeks ago she called him hysterical begging to come over bc she was miserable at her moms. Disclosed to us all kinds of information about how her moms has been treating her, throwing things at her and breaking things when she’s mad, cussing at her, calling her names, and leaving them home alone to bar hop and then the kids have to care for her drunk when she gets home. My fiancé filed a restraining order against her mother and they had an emergency hearing the other day which the judge was biased and claimed he saw no neglect. Since his daughter wanted to stay with us the judge issued a temporary order stating we have her for a month but she gets every other weekend visits with her mom, and also his son will be coming back and forth to us on the weekends. When we dropped her off for the weekend her mom was already with friends...I’m not sure what will happen at the next hearing at the beginning of next month but I feel so paranoid and stuck. I’m so uncomfortable with having the kids come back and forth between a house that takes no precautions and ours! No matter how small the risk...our county is in red...it could potentially put lives on the line if tbeir mom should come in contact with it and the kids come to our house. But we have no choice. My fiancé feels the same but he misses and loves his kids and can’t help but be all over them when they’re around...like a part of me wants him to demand at the next hearing that shit changes or we cannot have them over but I know it’s unreasonable....like I’m asking him to just continue not being part of his children’s lives until this blows over if it ever does...simply because their selfish mom doesn’t care whatsoever. He has asked her to stay at home and social distance but of course that’s a no go....again, I know some of you probably feel like I’m overreacting but I’m not willing to take any chances with my family and loved ones....I don’t feel like it’s a game. The risk is real and it’s there but it comes between the relationship of my man and his babies so where can the line be drawn? We are in a tough spot for sure...not looking for judgement or ridicule but how would you ladies feel and how would you handle the situation? Just need some words of encouragement or some help on the matter😩