It is always a difficult decision to have a rat put to sleep but I would rather let them go while they still have some quality of life, rather than see them suffer.
If the boys get a bit sniffly, I give them echinechea and goldenseal because it stimulates their immune system. I give them each one drop on bread, once a day for a week, then a week off.
Propolis is very good at healing up small wounds and scratches. It can be taken orally as well, so if they lick it off their fur, it won't hurt them.
Rescue Remedy is good to put in the water if you have new rats who are a bit nervous. I put about six drops in their water bottle. If a rat has had a shock then you can give them a drop on some bread or in a tiny amount of milk.