the safest way to treat kittens for fleas

I have 2 indoor cats and took in a pregnant stray cat. Well the stray cat had 5 kittens and are covered in fleas not to mention my cats are covered too. I'm taking my cats to the vet in the morning but how do I treat the stray and the kittens when they are still in the same house

I recommend frontline! Check with the vet for the dosage for the kittens and if they are to young to use it on them.
Not sure what the age is, but if you call any vet they will help you and give you advice and you won't have to bring them in!