Honey. Before the penicillin revolution, it was a common addition to poultices and the like.
It's a great antibiotic. I dunno how you can try to stock up for 12 ppl for 3 months. You're a blessing to them as you're thinking of if you can do it.

Can't they bring their own toilet paper, and similar dry goods, for a 3 month stay? That'd take some of the burden off of you.

Thanks!