Need some advice on children having possible covid exposure

Ok so I am going to try to cram a long story into a not so long post lol bare with me... my fiancé and I have 5 children combined, we each have two from a previous relationship and a 7 month old together! We’ve been together 3 years and since the beginning, his children’s mother (we’ll call her BM just to keep it short) has tried to making his relationship with them as difficult as possible! She has an auto immune disease herself and yet takes no precautions pertaining to COVID...tells the kids it’s no big deal, no worse than the flu and still allows them to hang out with multiple friends, go to nail salons, restaurants, around people and she’s regularly at the bar! For these reasons we have not had his children over for his regular visits in months! Other than once they came over for a couple hours bc my fiancé was dying not seeing them! We share the same fears of our baby who does not yet have built immunity contracting covid, our sweet elderly neighbors we help out...and my Father who recently finished chemo, had a heart attack a few years ago and this past year recovered from whooping cough and has damaged lungs from it! My Dad is my rock and the odds are against him if he should come in contact with covid...I won’t delve into that but my own children have not even been getting to spend time with their grandparents in fear of possibly being asymptomatic and spreading it...we don’t m go anywhere or hang out with anyone. We run to the store for necessities and stay home and try to do our part in not possibly spreading the disease! And yes I’m fully aware the recovery rate is good for most people, and the likelihood of babies having detrimental affects from it is low but regardless these are not risks I’m willing to take regardless of how small! I try to think of those that I love who may not be blessed with a good outcome should they get it! So anyway, my man is going through it, his children are begging to come around and he is constantly trying to explain to them why they can’t! His BM is telling them hesmaking excuses, plastering on fb that he’s abandoning them and caring for my children and not his own! It is such a shitty situation! Not to mention the fear of THEM getting it bc of her irresponsibility! Recently my fiancé contacted the guardian ad litem on their court case to talk about possibly getting temporary emergency custody...(where we would quarantine his kids for 2 weeks in another room and then allow them to socialize with everyone in the house)...I’m sure some of y’all think we are taking this overboard but again, we are trying to be extra precautious! It doesn’t seem like you have your children’s best interest at heart if you are continuously putting them in situations where you have no idea if those around them have been exposed or are asymptomatic...the guardian ad litem didn’t share our views, thinks it’s blown out of proportion and tried to explain to my man that babies are unlikely to get it and there’s no evidence of children being able to spread it, and urged him to research (which we have)...he said if my man wanted to go forth with it he would gather the paperwork and leave it up to the judge...he also added that even tho he doesn’t share the same views, he does support ours and does think he could still have a fighting chance in court! We live in a hotspot, granted in a small town and it’s not rampant, it’s still effecting people we know. Before we go forth with this, has anyone else gone through anything like this or have any advice or tips to help the situation? It seems like it will all come down to the judge and her perception of the pandemic...whether she is someone precautious or someone who views this as no big deal like seemingly most people do. I’m not sure if we really have a leg to stand on or a legitimate chance.