It is very important to treat your house as well as the animals.
Frontline is the best product and will work in conjunction with treating the house - as long as it is applied properly.
You must make sure it is applied directly onto the skin, not onto the hair (this refers to the "spot-on" version)
Reactions to frontline are uncommon. What usually happens if that cats groom some of the solution off either themselves or other cats in the house, which then can cause them to be unwell. Therefore it is important to apply it just behind the head on the neck where they can't lick, and also to separate cats for a while after treatment (same goes for dogs, although they tend not to groom as much).
For treating the house, I recommend a spray such as Acclaim, although there are many similar products. This will last for 12 months. It is also important to empty your hoover after every use, and to wash all bedding thoroughly.
Fish tanks are best covered while using these products, although there shouldn't be a problem once the spray has settled.
Treating your garden will have no effect, unless your cats never leave your garden, and no other animals enter. Most fleas are transferred to your pet by contact with other animals. After they have fleas, no treatment will be effective unless the source of re-infection (which will be fleas in your house) is dealt with.
Flea collars do not work.
They also tend to cause a lot more reactions than anything else.
It is also important to use only 1 flea treatment on your animals at a time.
So flea collars must be removed before any other treatment.
Hope this is useful.