I know that you have a lot of cats so do what I do. Just buy the largest dog advantage,over 55lbs, in the regular formula not the multi. Measure it out according to how much your cats weigh. I've been doing this for years and it works great and also saves me so much money. My former vet is the one who told me about this so it's very safe as long as you know how much your cats weigh.

Cats up to 9lbs get 0.4ml and cats over 9lbs get 0.8ml. I don't squirt it out all in one place but do it in about 3-4 places behind their head/neck area where they can't reach it. I use small syringes and mark the correct level with first-aid tape because over time the numbers will wear off. If you have any remaining, just put it a something you can keep covered so you can use it next time. Good luck.