Whoa.... hold on. You've been giving your boyfriend's lung medicine to the ferret? And mouthwash? And.. whipped cream?
I do hope I'm wrong about your BF's medicine being given to the ferret. No human medicine should ever be administered to an animal without a veterinarian's approval. The difference in dosages could be fatal, as could the side effects.
As your vet confirmed, mouth wash is deadly to a ferret. I don't know if this was given intentionally or by accident, but if intentionally, please never give mouth wash, toothpaste, etc. to an animal. It has massive amounts of alchohol and can cause renal failure and liver damage. If this was accidental, they make little child "locks" that can be placed on cabinet doors. They are def. a must-have for every ferret owner. Ferrets are curious and will get into everything; they need to be closely watched, and the house should be ferret proofed.
Finally... I would not reccomend whipped cream. Ferrets are carnivores and thus have a very hard time digesting the carbohydrates and sugars in whipped cream. It can cause GI upsets, and high sugar is bad for any animal. If you want to give him a treat to encourage him to eat following his ordeal, there are great products on the market like Ferravite, a palatable nutritional suppliment that encourages appetite and help the skin and coat. You can also give a little bit of canned cat food, but mostly stick to a pelleted diet formulated for ferrets.
Now, as for your tom cat, I would simply not allow him to come into contact with your ferrets. If he suceeds, he could harm them. Cats use their teeth for grip when mating. The bacteria in a cat's saliva can cause abcesses and serious infections in ferrets. Your best bet is to keep them apart.
Also, are your ferrets vaccinated? If the cat is an outdoor/indoor cat, he should be kept away from the ferrets unless they are vaccinated for distemper/rabies as he can carry viruses in on his hair-coat and transmit them to the ferrets.
Hope that helped! Please do not hesitate to email me with any other questions you have in the future.