Hopefully this is helpful. Sorry it's kind of long.
Fleas can be a very frustrating problem. If you see one adult flea, chances are, there's other adult fleas around. It doesn't sound like you have any dogs, just the cats and chins, so I'm going to focus on cat flea control.
Fleas can possibly infest the head and tails of chinchillas, but I'm not sure how much of a problem this unless you've got a severely infested household. I would concentrate on getting control of the cats. I also don't know if chins are a preferred host to fleas - the most common fleas in the US (cat fleas, with dog fleas being a distant second) will bite humans, but typically will move on to the dogs and cats in the household. Fleas can be brought indoors from the outside. Just cos a cat doesn't go outside doesn't mean the humans in the home, or the dog in the household, doesn't. Human-only homes have less of a problem with fleas because humans aren't preferred hosts, so don't reproduce fleas as well. If you go for a walk, walk by a bush where the local stray left a couple fleas, which jump onto your pantleg, and then leave you when you get home and find your cats - you've got fleas.
Once you have adult fleas in the household, they look for a preferred host (cats) and start to feed. Once they've been feeding, they will start laying eggs within 24 hours, and in one lifetime, lay hundreds of eggs. The eggs fall off the pet and into the dirt/carpet/whatever. Those eggs will hatch out into larvae in a week or so (less if conditions are right), and be little larvae wriggling around deep in your carpet/couch/whatever. The larvae eat (their favorite food is adult flea poop, which is partially digested blood), and then go into a pupa. In the right conditions, the pupa can hang out for about a week before hatching - but they can delay for up to a year. This is where you get the stories of people with no pets moving into a house that's been empty for months - but the previous people had pets. The fleas wait for triggers to emerge from the pupa (vibrations, slight increase in temperature, slight increase in local carbon dioxide concentration, etc - these are things that say "there's a mammal here!").
If you see one flea, there's probably a dozen that you didn't see. Fleas are uniquely suited to hiding deep in the fur of their hosts and not be seen.
What you want to do is make sure that your are stimulating as many fleas to come out as possible, and to make your cats into flea killing machines so that the adult fleas come out and DIE.
Advantage and Frontline are both great products. They kill the adult flea. The unfortunate thing is that neither kills them super fast, though they both should kill fast enough that the fleas aren't laying eggs. They ARE very effective (just not as fast as, say Capstar). The other unfortunate thing is that both products appear to start wearing off the cat at about the 3 week mark - they still kill fleas, but not quite as quickly and not quite as many as before.
Revolution is absorbed systemically, and seems to work a bit faster, and last a bit longer for killing adult fleas. It also has the advantage of working against intestinal parasites and heartworms (yes, indoor cats are at risk!). It's my personal favorite product, and what I use on my cats.
I don't know a lot about Advantage Multi and all the other newer products on the market (e.g., Vectra, Promeris, etc). If your vet carries them, they will know more about these products and the pros and cons of each.
Capstar is a great product, it can be a hassle. It's a pill you give the cat up to once a day. The effects seem to last about 24 hours. In a heavily flea-infested home, or in a severely flea-allergic cat, it works best if given at least 3 times a week. [Comfortis is a new product for dogs that's a pill lasting 30 days - it is not labelled for cats, though I've heard of a few people using it on outdoor cats (i.e., the ones most at risk of getting fleas and possibly more difficult to pill because more difficult to catch, so they put it in food) without ill effects. Personally, I'm not risking it til the company does all the safety work (rumors say they have) and gets the label approved.]
Program is an injection that is given every 6 months by a vet. It's flea birth control. It can be used in conjunction with any of the above (it was originally marketed with Capstar). It's sort of your clean-up committee. Any fleas that happen to survive your adulticides long enough to lay eggs won't be able to reproduce - none of the eggs will hatch. [For dogs, Sentinel is basically Program + Interceptor (heartworm/intestinal parasite control) as a monthly tablet. Program injection doesn't exist for dogs; Program tablet does exist for both species, but is pretty expensive].
If you use an adult killer (Advantage, Revolution, Frontline, Capstar) along with Program, you get to stop the flea life cycle in two different places. Revolution appears to have some effect against flea eggs; Frontline TopSpot is supposed to (I haven't personally looked at the data proving it, but it's labelled as such, so I'll believe them for now). There's a lot of other new products out - I just am not familiar with them.
Personally, I recommend Revolution +/- Program to get control of fleas in cats. I have one patient who gets to use Capstar and Revolution because of her flea allergies - the other cats in the house use Revolution. Some patients who can go to just Program over time (but then I have to recommend Interceptor for Cats to get the heartworms and intestinal parasites) - I know a vet who does this, because she finds it easier to pill her cat once a month and give her cat a shot every six months than do a topical once a month (she doesn't like the mess). I don't mind pilling my cats, but it's easier to do a topical for me. To each their own. Every vet probably has their own favorite group of products they use. Whichever you end up using - you're trying to turn your cat into a flea-free zone, and you want all the baby fleas to come out and visit the cat so they can die. If you use Frontline or Advantage, I'd use it every 3 weeks until the fleas are under control, then see if you can go to the every 4 weeks it's labelled for. Revolution seems to work just fine at the every 4 week dosing.
The OTC flea control products vary in effectiveness, toxicity issues, and dosing (i.e., they may or may not have what they're really supposed to have in them). They're typically older, cheaper, more toxic chemicals - work well against the flea, but some of them also work well against the cat. The dog formulations are typically more toxic (cats are very sensitive to certain types of chemicals). Flea collars pretty much only work at the location of the collar, not over the whole animal - and again, can be toxic.
You want to encourage the fleas to come out of the pupa and visit the cats. The easiest way to do this is to vacuum. Everywhere. Every day. Into corners, under furniture. Wash anything the pets have been on that can be washed, and vacuum the rest (pet beds, couch cushions, bed mattresses...) . You're trying to get the vibrations to stimulate the fleas to come out. Empty the bag (outside!) every day (here's somewhere to use the flea collar - in the garbage bag, to kill any fleas that have been sucked up). The more fleas you can get to come out of hiding, the faster they will come to the cats and DIE.
And then there's environmental control. Of course, getting the fleas under control will work faster if you can kill all the larvae and pupae and eggs hanging out in your carpet/couch/etc. Flea bombs, sprays, and other treatments for house and yard exist. Some people want to use them, some would rather not. Even if you don't - be diligent with the flea control on the cats - and you can have control over the fleas in a period of 3-6 months. Soemtimes more, sometimes less.
Talk to your vet. They will know what products work well in their hands, which products seem to work best against the local fleas, as well as be your source of all these products. I can only talk about the products I know - it's possible your vet doesn't carry one or more of these products, because they've found that something else does the trick
