Some people get this from their vets and some people order it online. That is what I chose to do. The place I ordered it from was in Austrilia and their website is : www.pets-megastore.com.au
I first asked my vet if they thought this was the best solution for my kitties.
As for what I do with my cats:
I went to my local Pharmacy (I actually work for one!) and bought a syringe with a removable needle. It needs to hold at least 1 ML. Then using masking tape, I mark the right dose on the syringe since the med will eat of the ink of the syringe. I then fill the syringe to the mark of the tape, then remove the needle. Then I part the cats fur and apply it in between their shoulder blades. My cats don't like it at all, so you might need someone to hold them down until you get it applied. You can get the dosage on that site that I gave you. I use .8ML per cat since they all weigh more than 9 pounds.
Since you only have 3 animals to treat, you will have left over med. I'm not sure what you need to do with it since usually I don't have any left over. The website says it should last 5 applications per tube, but I leak the stuff all over my hands so I only get 4 applications.
The Advantage that I use is the one for Dogs over 25 kg.
Hope this may help you out. Once again, I'd ask the Vet just in case before you do this. Don't want to hurt your little ones!