I'm right there with you Landis. I'm very new to this chicken thing - we lost our first three EEs to Mareks (unvaccinated) and now just today another pullet died unexpectedly - she was only here two months but she was vaccinated. I'm hopeful our remaining pullet will stay healthy, but she's the only one now - lonely for sure. I'm reluctant to bring in more birds. A vet that euthanized one of our hens told me many diseases are air borne and can travel many miles on the wind so if there are other chickens within a mile, we're hosed.
We've treated bumble foot, egg binding, vent gleet, sour crop, impacted crop, coccidiosis (which lives on your property for two years per the vet), respiratory illness and of course Marek's. So emotionally exhausting and financially disappointing at this point. We used to joke about eating our $5,000 eggs waiting for the start up cost ratio to work itself out. This chicken thing was supposed to be a fun adventure with yummy eggs. I think we've eaten maybe a dozen fresh eggs since February.
I wasn't prepared for all the heartache and didn't realize I had to be my own vet. I'm so grateful I stumbled upon this site. Honestly, had I seen all this information prior to getting chickens, I don't think I would have. But since I decided to jump in head first and learn on the fly, here we are.
I can't really answer your questions with any authority. Do what you think is right. If it were me, I would leave them interacting together because as you said, at this point, everyone is exposed.
Hugs of empathy.